Re: Linux mdadm superblock question.

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

>0.90 has a very bad problem, which is that it is hard to distinguish
>between a RAID partition at the end of volume and a full RAID device.
>This is because 0.90 doesn't actually tell you the start of the device.
>
>Then, of course, there are a lot of limitations on size, number of
>devices, and so on in 0.90.

but it is the only format supporting autodetection. 

So - when will autodetection be introduced with 1.X? And if not, why not?

All I found was 'autodetection might be troublesome' and nothing else.
 But dealing with initrds is troublesome too. Pure evil even. 

Glück Auf,
Volker

Re: Linux mdadm superblock question.

[Michael Evans]

On Sat, Feb 13, 2010 at 5:51 PM, Volker Armin Hemmann
<volkerarmin@googlemail.com> wrote:
>>0.90 has a very bad problem, which is that it is hard to distinguish
>>between a RAID partition at the end of volume and a full RAID device.
>>This is because 0.90 doesn't actually tell you the start of the device.
>>
>>Then, of course, there are a lot of limitations on size, number of
>>devices, and so on in 0.90.
>
> but it is the only format supporting autodetection.
>
> So - when will autodetection be introduced with 1.X? And if not, why not?
>
> All I found was 'autodetection might be troublesome' and nothing else.
>  But dealing with initrds is troublesome too. Pure evil even.
>
> Glück Auf,
> Volker
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

I remember hearing that 1.x had /no/ plans for kernel level
auto-detection ever.  That can be accomplished in early-userspace
leaving the code in the kernel much less complex, and therefore far
more reliable.

In other words, 'auto-detection' for 1.x format devices is using an
initrd/initramfs.

Re: Linux mdadm superblock question.

[david]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1542 bytes --]

On Sat, 13 Feb 2010, Michael Evans wrote:

> On Sat, Feb 13, 2010 at 5:51 PM, Volker Armin Hemmann
> <volkerarmin@googlemail.com> wrote:
>>> 0.90 has a very bad problem, which is that it is hard to distinguish
>>> between a RAID partition at the end of volume and a full RAID device.
>>> This is because 0.90 doesn't actually tell you the start of the device.
>>>
>>> Then, of course, there are a lot of limitations on size, number of
>>> devices, and so on in 0.90.
>>
>> but it is the only format supporting autodetection.
>>
>> So - when will autodetection be introduced with 1.X? And if not, why not?
>>
>> All I found was 'autodetection might be troublesome' and nothing else.
>>  But dealing with initrds is troublesome too. Pure evil even.
>>
>> Gl?ck Auf,
>> Volker
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
> I remember hearing that 1.x had /no/ plans for kernel level
> auto-detection ever.  That can be accomplished in early-userspace
> leaving the code in the kernel much less complex, and therefore far
> more reliable.
>
> In other words, 'auto-detection' for 1.x format devices is using an
> initrd/initramfs.

hmm, I've used 1.x formats without an initrd/initramfs (and without any 
conifg file on the server) and have had no problem with them being 
discovered. I haven't tried to use one for a boot/root device, so that may 
be the difference.

David Lang

Re: Linux mdadm superblock question.

[Michael Evans]

On Sat, Feb 13, 2010 at 11:21 PM,  <david@lang.hm> wrote:
> On Sat, 13 Feb 2010, Michael Evans wrote:
>
>> On Sat, Feb 13, 2010 at 5:51 PM, Volker Armin Hemmann
>> <volkerarmin@googlemail.com> wrote:
>>>>
>>>> 0.90 has a very bad problem, which is that it is hard to distinguish
>>>> between a RAID partition at the end of volume and a full RAID device.
>>>> This is because 0.90 doesn't actually tell you the start of the device.
>>>>
>>>> Then, of course, there are a lot of limitations on size, number of
>>>> devices, and so on in 0.90.
>>>
>>> but it is the only format supporting autodetection.
>>>
>>> So - when will autodetection be introduced with 1.X? And if not, why not?
>>>
>>> All I found was 'autodetection might be troublesome' and nothing else.
>>>  But dealing with initrds is troublesome too. Pure evil even.
>>>
>>> Gl?ck Auf,
>>> Volker
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>
>> I remember hearing that 1.x had /no/ plans for kernel level
>> auto-detection ever.  That can be accomplished in early-userspace
>> leaving the code in the kernel much less complex, and therefore far
>> more reliable.
>>
>> In other words, 'auto-detection' for 1.x format devices is using an
>> initrd/initramfs.
>
> hmm, I've used 1.x formats without an initrd/initramfs (and without any
> conifg file on the server) and have had no problem with them being
> discovered. I haven't tried to use one for a boot/root device, so that may
> be the difference.
>
> David Lang

Yes, that is the difference.  You must have a more traditional simple
block device and filesystem drivers compiled in.  You have no need for
extra drivers or higher level device detection and evaluation (with
user-set policies to determine operation).  Anything past root-fs
mount can happen in normal user-space before logins are enabled.

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Sonntag 14 Februar 2010, you wrote:

> 
> In other words, 'auto-detection' for 1.x format devices is using an
> initrd/initramfs.

which makes 1.x format useless for everybody who does not want to deal with 
initrd/initramfs.

Glück Auf,
Volker

Re: Linux mdadm superblock question.

[John Robinson]

On 14/02/2010 18:40, Volker Armin Hemmann wrote:
> On Sonntag 14 Februar 2010, you wrote:
> 
>> In other words, 'auto-detection' for 1.x format devices is using an
>> initrd/initramfs.
> 
> which makes 1.x format useless for everybody who does not want to deal with 
> initrd/initramfs.

True, but afaik every distro uses an initrd/initramfs and bundles tools 
making it easy to manage and customise them, so what's the problem?

Cheers,

John.

Re: Linux mdadm superblock question.

[Gabor Gombas]

On Sun, Feb 14, 2010 at 06:53:38PM +0000, John Robinson wrote:

> True, but afaik every distro uses an initrd/initramfs and bundles
> tools making it easy to manage and customise them, so what's the
> problem?

Distro provided initramfs generators have a bad habit assuming you
patch/build your kernel like the distro does. If you want to use a
vanilla kernel with different things built in/built as modules/not built
at all, then you can get nasty surprises, and debugging can be rather
painful.

My current view is if you use a distro kernel, then you should also use
an initramfs (in fact you do not have a choice). But if you want to
build your own kernel, then you should get rid of the initramfs.

Gabor

Re: Linux mdadm superblock question.

[Bill Davidsen]

Volker Armin Hemmann wrote:
> On Sonntag 14 Februar 2010, you wrote:
>
>   
>> In other words, 'auto-detection' for 1.x format devices is using an
>> initrd/initramfs.
>>     
>
> which makes 1.x format useless for everybody who does not want to deal with 
> initrd/initramfs.
>   

You make this sound like some major big deal. are you running your own 
distribution? In most cases mkinitrd does the right thing when you "make 
install" the kernel, and if you are doing something in the build so 
complex that it needs options, you really should understand the options 
and be sure you're doing what you want.

Generally this involves preloading a module or two, and if you need it 
every time you probably should have built it in, anyway.

My opinion...

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Dienstag 16 Februar 2010, Bill Davidsen wrote:
> Volker Armin Hemmann wrote:
> > On Sonntag 14 Februar 2010, you wrote:
> >> In other words, 'auto-detection' for 1.x format devices is using an
> >> initrd/initramfs.
> > 
> > which makes 1.x format useless for everybody who does not want to deal
> > with initrd/initramfs.
> 
> You make this sound like some major big deal. are you running your own
> distribution? In most cases mkinitrd does the right thing when you "make
> install" the kernel, and if you are doing something in the build so
> complex that it needs options, you really should understand the options
> and be sure you're doing what you want.
> 
> Generally this involves preloading a module or two, and if you need it
> every time you probably should have built it in, anyway.
> 
> My opinion...

I am running my own kernels - and of course everything that is needed to boot 
and get the basic system up is built in. Why should I make the disk drivers 
modules? 
That does not make sense.

And the reason is simple: even when the system is completely fucked up, I want 
a kernel that is able to boot until init=/bin/bb takes over.

Glück Auf
Volker

Re: Linux mdadm superblock question.

[Nick Bowler]

On 22:06 Tue 16 Feb     , Volker Armin Hemmann wrote:
> On Dienstag 16 Februar 2010, Bill Davidsen wrote:
> > Volker Armin Hemmann wrote:
> > > On Sonntag 14 Februar 2010, you wrote:
> > >> In other words, 'auto-detection' for 1.x format devices is using an
> > >> initrd/initramfs.
> > > 
> > > which makes 1.x format useless for everybody who does not want to deal
> > > with initrd/initramfs.
> > 
> > You make this sound like some major big deal. are you running your own
> > distribution? In most cases mkinitrd does the right thing when you "make
> > install" the kernel, and if you are doing something in the build so
> > complex that it needs options, you really should understand the options
> > and be sure you're doing what you want.
> > 
> > Generally this involves preloading a module or two, and if you need it
> > every time you probably should have built it in, anyway.
> > 
> > My opinion...
> 
> I am running my own kernels - and of course everything that is needed to boot 
> and get the basic system up is built in. Why should I make the disk drivers 
> modules? 
> That does not make sense.

I agree that it makes little sense to make something a module when you
can't unload it anyway, but...

> And the reason is simple: even when the system is completely fucked up, I want 
> a kernel that is able to boot until init=/bin/bb takes over.

I put a complete set of recovery tools into my initramfses so that when
the system is completely fucked up, I have a kernel that is able to boot
until rdinit=/bin/zsh (or /bin/bb, if you prefer) takes over.

This has the added advantage of working when the root filesystem cannot
be mounted at all: a scenario which does not seem too far-fetched when
the filesystem is located on a raid array.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Dienstag 16 Februar 2010, Nick Bowler wrote:
> On 22:06 Tue 16 Feb     , Volker Armin Hemmann wrote:
> > On Dienstag 16 Februar 2010, Bill Davidsen wrote:
> > > Volker Armin Hemmann wrote:
> > > > On Sonntag 14 Februar 2010, you wrote:
> > > >> In other words, 'auto-detection' for 1.x format devices is using an
> > > >> initrd/initramfs.
> > > > 
> > > > which makes 1.x format useless for everybody who does not want to
> > > > deal with initrd/initramfs.
> > > 
> > > You make this sound like some major big deal. are you running your own
> > > distribution? In most cases mkinitrd does the right thing when you
> > > "make install" the kernel, and if you are doing something in the build
> > > so complex that it needs options, you really should understand the
> > > options and be sure you're doing what you want.
> > > 
> > > Generally this involves preloading a module or two, and if you need it
> > > every time you probably should have built it in, anyway.
> > > 
> > > My opinion...
> > 
> > I am running my own kernels - and of course everything that is needed to
> > boot and get the basic system up is built in. Why should I make the disk
> > drivers modules?
> > That does not make sense.
> 
> I agree that it makes little sense to make something a module when you
> can't unload it anyway, but...
> 
> > And the reason is simple: even when the system is completely fucked up, I
> > want a kernel that is able to boot until init=/bin/bb takes over.
> 
> I put a complete set of recovery tools into my initramfses so that when
> the system is completely fucked up, I have a kernel that is able to boot
> until rdinit=/bin/zsh (or /bin/bb, if you prefer) takes over.
> 
> This has the added advantage of working when the root filesystem cannot
> be mounted at all: a scenario which does not seem too far-fetched when
> the filesystem is located on a raid array.

and what do you do if you have to boot from a cd/usb stick and need to access 
the raid?

Simple with auto assembling. Not so much without.

Glück Auf,
Volker

Re: Linux mdadm superblock question.

[Nick Bowler]

On 23:18 Tue 16 Feb     , Volker Armin Hemmann wrote:
> On Dienstag 16 Februar 2010, Nick Bowler wrote:
> > I put a complete set of recovery tools into my initramfses so that when
> > the system is completely fucked up, I have a kernel that is able to boot
> > until rdinit=/bin/zsh (or /bin/bb, if you prefer) takes over.
> > 
> > This has the added advantage of working when the root filesystem cannot
> > be mounted at all: a scenario which does not seem too far-fetched when
> > the filesystem is located on a raid array.
> 
> and what do you do if you have to boot from a cd/usb stick and need to access 
> the raid?
> 
> Simple with auto assembling. Not so much without.

The same initramfs can be used on a CD or USB stick.  If you were
referring to using someone else's CD or USB stick, then obviously
mdadm will need to be available.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[Ian Dall]

On Tue, 2010-02-16 at 23:18 +0100, Volker Armin Hemmann wrote:
> On Dienstag 16 Februar 2010, Nick Bowler wrote:
> > On 22:06 Tue 16 Feb     , Volker Armin Hemmann wrote:
> > > On Dienstag 16 Februar 2010, Bill Davidsen wrote:
> > > > Volker Armin Hemmann wrote:
> > > > > On Sonntag 14 Februar 2010, you wrote:
> > > > >> In other words, 'auto-detection' for 1.x format devices is using an
> > > > >> initrd/initramfs.
> > > > > 
> > > > > which makes 1.x format useless for everybody who does not want to
> > > > > deal with initrd/initramfs.
> > > > 
> > > > You make this sound like some major big deal. are you running your own
> > > > distribution? In most cases mkinitrd does the right thing when you
> > > > "make install" the kernel, and if you are doing something in the build
> > > > so complex that it needs options, you really should understand the
> > > > options and be sure you're doing what you want.
> > > > 
> > > > Generally this involves preloading a module or two, and if you need it
> > > > every time you probably should have built it in, anyway.
> > > > 
> > > > My opinion...
> > > 
> > > I am running my own kernels - and of course everything that is needed to
> > > boot and get the basic system up is built in. Why should I make the disk
> > > drivers modules?
> > > That does not make sense.
> > 
> > I agree that it makes little sense to make something a module when you
> > can't unload it anyway, but...
> > 
> > > And the reason is simple: even when the system is completely fucked up, I
> > > want a kernel that is able to boot until init=/bin/bb takes over.
> > 
> > I put a complete set of recovery tools into my initramfses so that when
> > the system is completely fucked up, I have a kernel that is able to boot
> > until rdinit=/bin/zsh (or /bin/bb, if you prefer) takes over.
> > 
> > This has the added advantage of working when the root filesystem cannot
> > be mounted at all: a scenario which does not seem too far-fetched when
> > the filesystem is located on a raid array.
> 
> and what do you do if you have to boot from a cd/usb stick and need to access 
> the raid?
> 
> Simple with auto assembling. Not so much without.

I'm not sure what the problem is. I've had to do this (because the disk
with grub on the MBR was the one that failed - now I put grub on them
all).

I booted of the fedora install disk in rescue mode. Told it not to try
and mount any system disks, got into a shell and ran mdadm -As 

I'm not sure what else a kernel auto-assemble would be expected to do
that mdadm -As wouldn't...


-- 
Ian Dall <ian@beware.dropbear.id.au>

Re: Linux mdadm superblock question.

[Mr. James W. Laferriere]

 	Hello Bill ,

On Tue, 16 Feb 2010, Bill Davidsen wrote:
> Volker Armin Hemmann wrote:
>> On Sonntag 14 Februar 2010, you wrote:
>>> In other words, 'auto-detection' for 1.x format devices is using an
>>> initrd/initramfs.
>>
>> which makes 1.x format useless for everybody who does not want to deal with 
>> initrd/initramfs.
>
> You make this sound like some major big deal. are you running your own 
> distribution? In most cases mkinitrd does the right thing when you "make 
> install" the kernel, and if you are doing something in the build so complex 
> that it needs options, you really should understand the options and be sure 
> you're doing what you want.
>
> Generally this involves preloading a module or two, and if you need it every 
> time you probably should have built it in, anyway.
>
> My opinion...
 	My Opinion as well .  That is one of the many reasons why I have my '/' 
autoassemble .  And do to this I am permanently stuck at 0.90 version of the 
raid table .  No big shakes for that .  But at sometime in the past there was a 
discussion to have the 0.90 raid table be removed ,  NOW THAT SCARES THE H?LL 
OUT OF ME .  So far Neil has not done so .

 	I am unaware of any record from Neil or other maintainer(s) of the 
/md/ device tree saying that they will not remove the 0.90 table and the 
autoassembly functions there .  I'd very much like to hear a statement saying 
there will not be a removal of the autoassembly functions for 0.90 raid table 
from the kernel tree .

 		Tia ,  JimL
-- 
+------------------------------------------------------------------+
| James   W.   Laferriere | System    Techniques | Give me VMS     |
| Network&System Engineer | 3237     Holden Road |  Give me Linux  |
| babydr@baby-dragons.com | Fairbanks, AK. 99709 |   only  on  AXP |
+------------------------------------------------------------------+

Re: Linux mdadm superblock question.

[Neil Brown]

On Tue, 16 Feb 2010 16:03:43 -0900 (AKST)
"Mr. James W. Laferriere" <babydr@baby-dragons.com> wrote:

>  	Hello Bill ,
> 
> On Tue, 16 Feb 2010, Bill Davidsen wrote:
> > Volker Armin Hemmann wrote:
> >> On Sonntag 14 Februar 2010, you wrote:
> >>> In other words, 'auto-detection' for 1.x format devices is using an
> >>> initrd/initramfs.
> >>
> >> which makes 1.x format useless for everybody who does not want to deal with 
> >> initrd/initramfs.
> >
> > You make this sound like some major big deal. are you running your own 
> > distribution? In most cases mkinitrd does the right thing when you "make 
> > install" the kernel, and if you are doing something in the build so complex 
> > that it needs options, you really should understand the options and be sure 
> > you're doing what you want.
> >
> > Generally this involves preloading a module or two, and if you need it every 
> > time you probably should have built it in, anyway.
> >
> > My opinion...
>  	My Opinion as well .  That is one of the many reasons why I have my '/' 
> autoassemble .  And do to this I am permanently stuck at 0.90 version of the 
> raid table .  No big shakes for that .  But at sometime in the past there was a 
> discussion to have the 0.90 raid table be removed ,  NOW THAT SCARES THE H?LL 
> OUT OF ME .  So far Neil has not done so .
> 
>  	I am unaware of any record from Neil or other maintainer(s) of the 
> /md/ device tree saying that they will not remove the 0.90 table and the 
> autoassembly functions there .  I'd very much like to hear a statement saying 
> there will not be a removal of the autoassembly functions for 0.90 raid table 
> from the kernel tree .

I will not be removing 0.90 or auto-assemble from the kernel in the
foreseeable future.
None the less, I recommend weaning yourself from your dependence on it.
initramfs is the future, embrace it.

NeilBrown

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Mittwoch 17 Februar 2010, Neil Brown wrote:

> I will not be removing 0.90 or auto-assemble from the kernel in the
> foreseeable future.
> None the less, I recommend weaning yourself from your dependence on it.
> initramfs is the future, embrace it.
> 
> NeilBrown

a future that is worse than the present. For what reason?

Glück Auf,
Volker

Re: Linux mdadm superblock question.

[Neil Brown]

On Wed, 17 Feb 2010 03:38:46 +0100
Volker Armin Hemmann <volkerarmin@googlemail.com> wrote:

> On Mittwoch 17 Februar 2010, Neil Brown wrote:
> 
> > I will not be removing 0.90 or auto-assemble from the kernel in the
> > foreseeable future.
> > None the less, I recommend weaning yourself from your dependence on it.
> > initramfs is the future, embrace it.
> > 
> > NeilBrown
> 
> a future that is worse than the present. For what reason?

Reason: some things are easier to implement and maintain in userspace.
Implementing them in the kernel would likely produce a worse products.

Worse than the present:  only if you refuse to embrace it and there-by
contribute to fixing/improving it.

NeilBrown

Re: Linux mdadm superblock question.

[Kyle Moffett]

On Tue, Feb 16, 2010 at 21:01, Neil Brown <neilb@suse.de> wrote:
> On Tue, 16 Feb 2010 16:03:43 -0900 (AKST) "Mr. James W. Laferriere" <babydr@baby-dragons.com> wrote:
>>       I am unaware of any record from Neil or other maintainer(s) of the
>> /md/ device tree saying that they will not remove the 0.90 table and the
>> autoassembly functions there .  I'd very much like to hear a statement saying
>> there will not be a removal of the autoassembly functions for 0.90 raid table
>> from the kernel tree .
>
> I will not be removing 0.90 or auto-assemble from the kernel in the
> foreseeable future.
> None the less, I recommend weaning yourself from your dependence on it.
> initramfs is the future, embrace it.

What are people's reasons for pushback against initramfs?  I've heard
lots of claims that "it's not trustworthy" and "it breaks", but in 7
years of running bootable software RAID boxes on weird architectures
(even running Debian unstable) I have only once or twice had initramfs
problems.

As a software capability, initramfs makes it possible to use
*anything* as a root filesystem, no matter what is necessary to set it
up.  For example, I have seen somebody use DRBD (essentially network
RAID-1) as a root filesystem with a few custom hook scripts added to
the initramfs-tools configs.  Other examples include using Sun ZFS as
a root fs via an initramfs FUSE daemon, a feat which even Solaris
could not accomplish at the time.  Encrypted root filesystems also
require an initramfs to prompt for encryption keys and decrypt the
block device.  Multipath block devices are another example.

You should also take a look at your distro installers.  There is not a
single one made in the last several years which does not use an
initramfs to start networking or access the installation media.  In
fact, of all the distro installers I have had the most consistent
behavior regardless of system hardware from the ones which operate
entirely out of their initramfs.

>From a reliability perspective, an initramfs is no more essential
than, say, /sbin/init or /boot/vmlinuz-2.6.33.  Furthermore, all of
the modern initramfs generation tools automatically keep backup copies
exactly the same way that "make install" keeps backup copies of your
kernel images.  The two times I've managed to hose my initramfs I was
able to simply edit my grub config to use a file called something like
"/boot/initramfs-2.6.33.bak" instead.

In fact, I have had several times where an initramfs made my boot
process *more* reliable.  On one of my LVM JBOD systems, I was able to
pull a group of 3 SATA drives whose backplane had failed and drop them
all in USB enclosures to get the system back up and running in a half
an hour.  With just straight partitions on the volumes I would have
been hunting around for 2 hours to figure out where all my partitions
had gone only to have the USB drives spin up in a different order
during the next reboot.

If you're really concerned about boot-process reliability, go ahead
and tell your initramfs tool to include a fully-featured busybox,
coreutils, bash, strace, gdb, and a half-dozen other developer tools.
You may wait an extra 20 seconds for your bootloader to load the damn
thing during boot, but you'll be able to track down that annoying
10-second hang in your /sbin/init program during config-file parsing.

I've built specialized embedded computers with stripped-down chipset
initialization code, a tiny Linux kernel and a special-purpose
initramfs burned into the flash.  By using the fastboot patches and
disabling all the excess drivers, my kernel was fully operational
within the first half-second.  It used the tools on the initramfs to
poke around on the hard disk as a bootloader, then kexec() to load the
operational kernel.

Counting up all the problems I've had with system boot... I've had an
order of magnitude more problems from somebody getting careless with
"rm", "dpkg --purge", etc than with initramfs deficiencies.

Cheers,
Kyle Moffett

Re: Linux mdadm superblock question.

[Rudy Zijlstra]

Kyle Moffett wrote:
> On Tue, Feb 16, 2010 at 21:01, Neil Brown <neilb@suse.de> wrote:
>   
>> On Tue, 16 Feb 2010 16:03:43 -0900 (AKST) "Mr. James W. Laferriere" <babydr@baby-dragons.com> wrote:
>>     
>>>       I am unaware of any record from Neil or other maintainer(s) of the
>>> /md/ device tree saying that they will not remove the 0.90 table and the
>>> autoassembly functions there .  I'd very much like to hear a statement saying
>>> there will not be a removal of the autoassembly functions for 0.90 raid table
>>> from the kernel tree .
>>>       
>> I will not be removing 0.90 or auto-assemble from the kernel in the
>> foreseeable future.
>> None the less, I recommend weaning yourself from your dependence on it.
>> initramfs is the future, embrace it.
>>     
>
> What are people's reasons for pushback against initramfs?  I've heard
> lots of claims that "it's not trustworthy" and "it breaks", but in 7
> years of running bootable software RAID boxes on weird architectures
> (even running Debian unstable) I have only once or twice had initramfs
> problems.
>
> As a software capability, initramfs makes it possible to use
> *anything* as a root filesystem, no matter what is necessary to set it
> up.  For example, I have seen somebody use DRBD (essentially network
> RAID-1) as a root filesystem with a few custom hook scripts added to
> the initramfs-tools configs.  Other examples include using Sun ZFS as
> a root fs via an initramfs FUSE daemon, a feat which even Solaris
> could not accomplish at the time.  Encrypted root filesystems also
> require an initramfs to prompt for encryption keys and decrypt the
> block device.  Multipath block devices are another example.
>
> You should also take a look at your distro installers.  There is not a
> single one made in the last several years which does not use an
> initramfs to start networking or access the installation media.  In
> fact, of all the distro installers I have had the most consistent
> behavior regardless of system hardware from the ones which operate
> entirely out of their initramfs.
>
> From a reliability perspective, an initramfs is no more essential
> than, say, /sbin/init or /boot/vmlinuz-2.6.33.  Furthermore, all of
> the modern initramfs generation tools automatically keep backup copies
> exactly the same way that "make install" keeps backup copies of your
> kernel images.  The two times I've managed to hose my initramfs I was
> able to simply edit my grub config to use a file called something like
> "/boot/initramfs-2.6.33.bak" instead.
>
> In fact, I have had several times where an initramfs made my boot
> process *more* reliable.  On one of my LVM JBOD systems, I was able to
> pull a group of 3 SATA drives whose backplane had failed and drop them
> all in USB enclosures to get the system back up and running in a half
> an hour.  With just straight partitions on the volumes I would have
> been hunting around for 2 hours to figure out where all my partitions
> had gone only to have the USB drives spin up in a different order
> during the next reboot.
>
> If you're really concerned about boot-process reliability, go ahead
> and tell your initramfs tool to include a fully-featured busybox,
> coreutils, bash, strace, gdb, and a half-dozen other developer tools.
> You may wait an extra 20 seconds for your bootloader to load the damn
> thing during boot, but you'll be able to track down that annoying
> 10-second hang in your /sbin/init program during config-file parsing.
>
> I've built specialized embedded computers with stripped-down chipset
> initialization code, a tiny Linux kernel and a special-purpose
> initramfs burned into the flash.  By using the fastboot patches and
> disabling all the excess drivers, my kernel was fully operational
> within the first half-second.  It used the tools on the initramfs to
> poke around on the hard disk as a bootloader, then kexec() to load the
> operational kernel.
>
> Counting up all the problems I've had with system boot... I've had an
> order of magnitude more problems from somebody getting careless with
> "rm", "dpkg --purge", etc than with initramfs deficiencies.
>
>
>   
We are looking at 2 different use-cases i think.

for the power-user system manager, who manages all his servers and has 
knowledgeable backup, initrd may indeed work as above.

I have to keep in mind, that when there is a problem while i am 
travelling (and that happens), there is no sys-admin present. Also, i am 
supporting systems remote where no-one has the knowledge to debug using 
a initrd. In such cases, initrd is an additional step. And each 
additional step is an additional source of mistakes.

1/ distro tools assume that the kernel being build will run on that 
machine. For servers this is often not true. There are very valid 
security reasons to exclude compilation capability from many servers.
2/ For most small shops, there is need for RAID (disks are fallible, 
shop cannot do without server), the RAID should work without being 
visible. If there is a problem with the RAID that causes auto-assemble 
to break, it means i need to travel (>100KM) to trouble shoot. The 
simpler the setup, the more i like it. This is also why i almost always 
use HW raid for the system partitions. The ones i use have userland 
tools in Linux which warn on disk failure, ensure auto rebuild, etc...
Still, for large storage needs it is SW RAID over SATA.
3/ for my home systems, if i need to remote-support to get things 
working again (i am often travelling for my work), the added layer of 
initrd is an added layer of possible mistakes.



Cheers,


Rudy

Re: Linux mdadm superblock question.

[Frans Pop]

Rudy Zijlstra wrote:
> 1/ distro tools assume that the kernel being build will run on that
> machine. For servers this is often not true. There are very valid
> security reasons to exclude compilation capability from many servers.

That's simply not true, at least not for Debian. If you actually use the 
distro tools [1] the only assumptions are made at kernel *installation* 
time, not at kernel build time.

I've been using initramfs-tools generated initrds for years without 
problems, and that includes "root on LVM on LUKS encrypted partition" 
and "root on LVM on RAID" setups.

Cheers,
FJP

[1] I.e. if you build and install the kernel as a .deb package using e.g. 
the deb-pkg target or kernel-package.

Re: Linux mdadm superblock question.

[Gabor Gombas]

On Wed, Feb 17, 2010 at 02:26:46PM +0100, Frans Pop wrote:

> That's simply not true, at least not for Debian. If you actually use the 
> distro tools [1] the only assumptions are made at kernel *installation* 
> time, not at kernel build time.

And that's why network-booted diskless clients and virtual guests have
all sort of useless modules loaded; the HW where the kernel package was
installed in this case is very different from the HW where the kernel
will run. If only there were a switch to prohibit ever looking at the
current machine's configuration when generating the initramfs...

> I've been using initramfs-tools generated initrds for years without 
> problems, and that includes "root on LVM on LUKS encrypted partition" 
> and "root on LVM on RAID" setups.

I've tried a couple of times to use a Debian-built initramfs with a
custom built kernel. The kernel worked fine without an initramfs (it had
everything built in), but it did not boot with the initramfs.

Gabor

Re: Linux mdadm superblock question.

[Frans Pop]

On Wednesday 17 February 2010, Gabor Gombas wrote:
> On Wed, Feb 17, 2010 at 02:26:46PM +0100, Frans Pop wrote:
> > That's simply not true, at least not for Debian. If you actually use
> > the distro tools [1] the only assumptions are made at kernel
> > *installation* time, not at kernel build time.
>
> And that's why network-booted diskless clients and virtual guests have
> all sort of useless modules loaded; the HW where the kernel package was
> installed in this case is very different from the HW where the kernel
> will run.

Interesting use case. But also a use case for which initramfs-tools 
probably very simply was never intended.

I agree that in this case you probably want to either
- have a very generic initrd that supports anything (Debian default) [1]
or
- provide a list of modules to include in the initrd based on knowing the
  hardware you want to support (e.g. using /etc/initramfs-tools/modules)
  and prevent including anything based on the host system.

I've never really done that so I don't know if initramfs-tools has any 
features to support that.

> If only there were a switch to prohibit ever looking at the 
> current machine's configuration when generating the initramfs...

Did you ever file a wishlist bug report for that?

> > I've been using initramfs-tools generated initrds for years without
> > problems, and that includes "root on LVM on LUKS encrypted partition"
> > and "root on LVM on RAID" setups.
>
> I've tried a couple of times to use a Debian-built initramfs with a
> custom built kernel. The kernel worked fine without an initramfs (it had
> everything built in), but it did not boot with the initramfs.

It's obviously hard to comment on something like this without more details 
(which would be off-topic for this list).


[1] Could still leave you with problems if the clients use something fancy 
for the root fs that uses info copied from /etc.

Re: Linux mdadm superblock question.

[Goswin von Brederlow]

Gabor Gombas <gombasg@digikabel.hu> writes:

> On Wed, Feb 17, 2010 at 02:26:46PM +0100, Frans Pop wrote:
>
>> That's simply not true, at least not for Debian. If you actually use the 
>> distro tools [1] the only assumptions are made at kernel *installation* 
>> time, not at kernel build time.
>
> And that's why network-booted diskless clients and virtual guests have
> all sort of useless modules loaded; the HW where the kernel package was
> installed in this case is very different from the HW where the kernel
> will run. If only there were a switch to prohibit ever looking at the
> current machine's configuration when generating the initramfs...

>From my experience you must boot up your client/guest and install the
kernel in there. Then copy the kernel and initrmafs over to the boot
server for use.

Initramfs was never designed to generate an image for another system, or
worse, for a pool of different systems. You can probably make it work on
a case by case basis but that wasn't thought of during the design phase.

Interesting idea though.

>> I've been using initramfs-tools generated initrds for years without 
>> problems, and that includes "root on LVM on LUKS encrypted partition" 
>> and "root on LVM on RAID" setups.
>
> I've tried a couple of times to use a Debian-built initramfs with a
> custom built kernel. The kernel worked fine without an initramfs (it had
> everything built in), but it did not boot with the initramfs.
>
> Gabor

'make-kpkg ... --initrd kernel-image' should build you your custom
kernel with all the magic required to generate a working initramfs.
If not then please do file bugs.

MfG
        Goswin

Re: Linux mdadm superblock question.

[Kyle Moffett]

On Wed, Feb 17, 2010 at 04:38, Rudy Zijlstra
<rudy@grumpydevil.homelinux.org> wrote:
> Kyle Moffett wrote:
>> On Tue, Feb 16, 2010 at 21:01, Neil Brown <neilb@suse.de> wrote:
>>> I will not be removing 0.90 or auto-assemble from the kernel in the
>>> foreseeable future.
>>> None the less, I recommend weaning yourself from your dependence on it.
>>> initramfs is the future, embrace it.
>>>
>>
>> What are people's reasons for pushback against initramfs?  I've heard
>> lots of claims that "it's not trustworthy" and "it breaks", but in 7
>> years of running bootable software RAID boxes on weird architectures
>> (even running Debian unstable) I have only once or twice had initramfs
>> problems.
>>
>> As a software capability, initramfs makes it possible to use
>> *anything* as a root filesystem, no matter what is necessary to set it
>> up.  For example, I have seen somebody use DRBD (essentially network
>> RAID-1) as a root filesystem with a few custom hook scripts added to
>> the initramfs-tools configs.  Other examples include using Sun ZFS as
>> a root fs via an initramfs FUSE daemon, a feat which even Solaris
>> could not accomplish at the time.  Encrypted root filesystems also
>> require an initramfs to prompt for encryption keys and decrypt the
>> block device.  Multipath block devices are another example.
>
> We are looking at 2 different use-cases i think.
>
> for the power-user system manager, who manages all his servers and has
> knowledgeable backup, initrd may indeed work as above.
>
> I have to keep in mind, that when there is a problem while i am travelling
> (and that happens), there is no sys-admin present. Also, i am supporting
> systems remote where no-one has the knowledge to debug using a initrd. In
> such cases, initrd is an additional step. And each additional step is an
> additional source of mistakes.

Actually, a properly built initramfs gives you far more reliable
behavior even without a local sysadmin.  For example, most
graphical-boot tools are designed to be built into an initramfs; I
have seen some prototype initramfs images which provide end-user
accessible GUI boot menus and other tools which function reliably even
when your root filesystem is inaccessible.

> 1/ distro tools assume that the kernel being build will run on that machine.
> For servers this is often not true. There are very valid security reasons to
> exclude compilation capability from many servers.

As Frans Pop states, this is entirely untrue for (at the very least)
Debian.  The "initramfs-tools" package present there works regardless
of where I obtain my kernel.  If I use the "make-kpkg" Debian tool
when building my kernel (regardless of where it is built), then the
resulting package will automatically generate an appropriate initramfs
image when installed.  If for some reason I install a kernel by hand I
can very trivially build the necessary initramfs with this command:

update-initramfs -c -k 2.6.32-mykernel01

In the event that you need to "customize" the initramfs for some
reason, you can simply do so.  When the "update-initramfs" tool is
next run, it will report that the user has customized that image and
avoid modifying it.  If you wish to return to the autogenerated
initramfs you can simply run this command:

update-initramfs -u -t -k 2.6.32-2-amd64

> 2/ For most small shops, there is need for RAID (disks are fallible, shop
> cannot do without server), the RAID should work without being visible. If
> there is a problem with the RAID that causes auto-assemble to break, it
> means i need to travel (>100KM) to trouble shoot. The simpler the setup, the
> more i like it. This is also why i almost always use HW raid for the system
> partitions. The ones i use have userland tools in Linux which warn on disk
> failure, ensure auto rebuild, etc...
> Still, for large storage needs it is SW RAID over SATA.
>
> 3/ for my home systems, if i need to remote-support to get things working
> again (i am often travelling for my work), the added layer of initrd is an
> added layer of possible mistakes.

You are actually just setting yourself up for problems.  RAID
autoassembly has bad corner cases when disks disappear between reboots
(which happens with failing disk head assemblies).  In that case it
will fail to find its root filesystem or wait forever for the last
disk to show up.  I have had even *worse* problems (including
corruption of unrelated logical volumes) with many hardware RAID
controllers, even those from big-name server vendors such as HP and
Dell.

To contrast, an initramfs is configurable to prompt the user,
automatically degrade the array after a small delay, or even play a
kazoo if desired :-D.  One of these days I may get around to building
myself a small GUI wrapper around mdadm on an initramfs which allows a
user to manually recover from RAID problems.

Cheers,
Kyle Moffett

Re: Linux mdadm superblock question.

[david]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1196 bytes --]

On Wed, 17 Feb 2010, Kyle Moffett wrote:

> On Wed, Feb 17, 2010 at 04:38, Rudy Zijlstra
> <rudy@grumpydevil.homelinux.org> wrote:
>> Kyle Moffett wrote:
>>> On Tue, Feb 16, 2010 at 21:01, Neil Brown <neilb@suse.de> wrote:
>>>> I will not be removing 0.90 or auto-assemble from the kernel in the
>>>> foreseeable future.
>>>> None the less, I recommend weaning yourself from your dependence on it.
>>>> initramfs is the future, embrace it.
>>>>
>>>
>>> What are people's reasons for pushback against initramfs?  I've heard
>>> lots of claims that "it's not trustworthy" and "it breaks", but in 7
>>> years of running bootable software RAID boxes on weird architectures
>>> (even running Debian unstable) I have only once or twice had initramfs
>>> problems.

Kyle,
   for a distro that is trying to make one kernel image run on every 
possible type of hardware features like initramfs (and udev, modeules, 
etc) are wonderful.

however for people who run systems that are known ahead of time and 
static (and who build their own kernels instead of just relying on the 
distro default kernel), all of this is unnessesary complication, which 
leaves more room for problems to creep in.

David Lang

Re: Linux mdadm superblock question.

[Nick Bowler]

On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> for a distro that is trying to make one kernel image run on every
> possible type of hardware features like initramfs (and udev, modeules,
> etc) are wonderful.
> 
> however for people who run systems that are known ahead of time and
> static (and who build their own kernels instead of just relying on the
> distro default kernel), all of this is unnessesary complication, which
> leaves more room for problems to creep in.

Such people can easily construct an initramfs containing busybox and
mdadm with a shell script hardcoded to mount their root fs and run
switch_root.  It's a ~10 minute jobbie that only needs to be done once.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Mittwoch 17 Februar 2010, Nick Bowler wrote:
> On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> > for a distro that is trying to make one kernel image run on every
> > possible type of hardware features like initramfs (and udev, modeules,
> > etc) are wonderful.
> > 
> > however for people who run systems that are known ahead of time and
> > static (and who build their own kernels instead of just relying on the
> > distro default kernel), all of this is unnessesary complication, which
> > leaves more room for problems to creep in.
> 
> Such people can easily construct an initramfs containing busybox and
> mdadm with a shell script hardcoded to mount their root fs and run
> switch_root.  It's a ~10 minute jobbie that only needs to be done once.


and even better when you don't have to do that one time job at all.

btw, what about additional delay? 


Glück Auf,
Volker

Re: Linux mdadm superblock question.

[Nick Bowler]

On 19:27 Wed 17 Feb     , Volker Armin Hemmann wrote:
> On Mittwoch 17 Februar 2010, Nick Bowler wrote:
> > On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> > > for a distro that is trying to make one kernel image run on every
> > > possible type of hardware features like initramfs (and udev, modeules,
> > > etc) are wonderful.
> > > 
> > > however for people who run systems that are known ahead of time and
> > > static (and who build their own kernels instead of just relying on the
> > > distro default kernel), all of this is unnessesary complication, which
> > > leaves more room for problems to creep in.
> > 
> > Such people can easily construct an initramfs containing busybox and
> > mdadm with a shell script hardcoded to mount their root fs and run
> > switch_root.  It's a ~10 minute jobbie that only needs to be done once.
> 
> and even better when you don't have to do that one time job at all.

But people who are building their own kernels are already doing a
(much harder, imo) one time job of configuring their kernels.

> btw, what about additional delay? 

It takes about half a second for mdadm to assemble my root array, is
that what you're referring to?

I assume that kernel auto-assembly is no faster, although I've never
used it.  Regardless, half a second isn't very long to wait.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[david]

On Wed, 17 Feb 2010, Nick Bowler wrote:

> On 19:27 Wed 17 Feb     , Volker Armin Hemmann wrote:
>> On Mittwoch 17 Februar 2010, Nick Bowler wrote:
>>> On 09:41 Wed 17 Feb     , david@lang.hm wrote:
>>>> for a distro that is trying to make one kernel image run on every
>>>> possible type of hardware features like initramfs (and udev, modeules,
>>>> etc) are wonderful.
>>>>
>>>> however for people who run systems that are known ahead of time and
>>>> static (and who build their own kernels instead of just relying on the
>>>> distro default kernel), all of this is unnessesary complication, which
>>>> leaves more room for problems to creep in.
>>>
>>> Such people can easily construct an initramfs containing busybox and
>>> mdadm with a shell script hardcoded to mount their root fs and run
>>> switch_root.  It's a ~10 minute jobbie that only needs to be done once.
>>
>> and even better when you don't have to do that one time job at all.
>
> But people who are building their own kernels are already doing a
> (much harder, imo) one time job of configuring their kernels.
>
>> btw, what about additional delay?
>
> It takes about half a second for mdadm to assemble my root array, is
> that what you're referring to?
>
> I assume that kernel auto-assembly is no faster, although I've never
> used it.  Regardless, half a second isn't very long to wait.

If you are aiming for a 5-second boot time it's 10% of your total boot 
time. That's a lot for a feature that's not needed.

David Lang

Re: Linux mdadm superblock question.

[Nick Bowler]

On 10:41 Wed 17 Feb     , david@lang.hm wrote:
> On Wed, 17 Feb 2010, Nick Bowler wrote:
> > It takes about half a second for mdadm to assemble my root array, is
> > that what you're referring to?
> >
> > I assume that kernel auto-assembly is no faster, although I've never
> > used it.  Regardless, half a second isn't very long to wait.
> 
> If you are aiming for a 5-second boot time it's 10% of your total boot 
> time. That's a lot for a feature that's not needed.

Only if the kernel auto-assembly takes zero time, which it obviously
does not.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[david]

On Wed, 17 Feb 2010, Nick Bowler wrote:

> On 10:41 Wed 17 Feb     , david@lang.hm wrote:
>> On Wed, 17 Feb 2010, Nick Bowler wrote:
>>> It takes about half a second for mdadm to assemble my root array, is
>>> that what you're referring to?
>>>
>>> I assume that kernel auto-assembly is no faster, although I've never
>>> used it.  Regardless, half a second isn't very long to wait.
>>
>> If you are aiming for a 5-second boot time it's 10% of your total boot
>> time. That's a lot for a feature that's not needed.
>
> Only if the kernel auto-assembly takes zero time, which it obviously
> does not.

the assembly time would probably be the same, but the initramfs being 
proposed did not include that time either.

David Lang

Re: Linux mdadm superblock question.

[Nick Bowler]

On 13:17 Wed 17 Feb     , david@lang.hm wrote:
> On Wed, 17 Feb 2010, Nick Bowler wrote:
> 
> > On 10:41 Wed 17 Feb     , david@lang.hm wrote:
> >> On Wed, 17 Feb 2010, Nick Bowler wrote:
> >>> It takes about half a second for mdadm to assemble my root array, is
> >>> that what you're referring to?
> >>>
> >>> I assume that kernel auto-assembly is no faster, although I've never
> >>> used it.  Regardless, half a second isn't very long to wait.
> >>
> >> If you are aiming for a 5-second boot time it's 10% of your total boot
> >> time. That's a lot for a feature that's not needed.
> >
> > Only if the kernel auto-assembly takes zero time, which it obviously
> > does not.
> 
> the assembly time would probably be the same, but the initramfs being 
> proposed did not include that time either.

This was the *only* time that was included.  Quoting myself:

> It takes about half a second for mdadm to assemble my root array

I didn't make any claim about any other timings, since I have not made
any measurements (I am not adding instrumentation code to my initramfs
and rebooting the box just to do this, and my watch is not precise
enough to measure the time spent in initramfs).

After the kernel has loaded, but before init on my root fs is run, there
are only three things that cause noticeable delays:

 * probing all the disks.
 * assembling the root array.
 * mounting the root filesystem.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[david]

On Wed, 17 Feb 2010, Nick Bowler wrote:

> On 13:17 Wed 17 Feb     , david@lang.hm wrote:
>> On Wed, 17 Feb 2010, Nick Bowler wrote:
>>
>>> On 10:41 Wed 17 Feb     , david@lang.hm wrote:
>>>> On Wed, 17 Feb 2010, Nick Bowler wrote:
>>>>> It takes about half a second for mdadm to assemble my root array, is
>>>>> that what you're referring to?
>>>>>
>>>>> I assume that kernel auto-assembly is no faster, although I've never
>>>>> used it.  Regardless, half a second isn't very long to wait.
>>>>
>>>> If you are aiming for a 5-second boot time it's 10% of your total boot
>>>> time. That's a lot for a feature that's not needed.
>>>
>>> Only if the kernel auto-assembly takes zero time, which it obviously
>>> does not.
>>
>> the assembly time would probably be the same, but the initramfs being
>> proposed did not include that time either.
>
> This was the *only* time that was included.  Quoting myself:
>
>> It takes about half a second for mdadm to assemble my root array

sorry, I misunderstood, I thought you were referring to the time added by 
using the initramfs itself.

David Lang

boot times, not mdadm (was: Linux mdadm superblock question.)

[martin f krafft]

[-- Attachment #1: Type: text/plain, Size: 988 bytes --]

also sprach Nick Bowler <nbowler@elliptictech.com> [2010.02.18.1037 +1300]:
> > the assembly time would probably be the same, but the initramfs being 
> > proposed did not include that time either.
> 
> This was the *only* time that was included.  Quoting myself:

If you are discussing boot times rather than mdadm, might I suggest
you change the subject line?

Upstream is keen on finally dropping kernel autoassembly, and
I support that because of the gained flexibility. Boot times are
important for laptops and desktops, which are hardly the primary
target of RAID.

Anyway, this is FLOSS. If you want kernel autoassembly, take over
the code and bring it up to speed.

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
"what's your conceptual continuity? --
 well, it should be easy to see:
 the crux of the bisquit is the apopstrophe!"
                                                        -- frank zappa
 
spamtraps: madduck.bogus@madduck.net

[-- Attachment #2: Digital signature (see http://martin-krafft.net/gpg/) --]
[-- Type: application/pgp-signature, Size: 198 bytes --]

Re: (boot time consequences of) Linux mdadm superblock question.

[Neil Brown]

On Wed, 17 Feb 2010 10:41:34 -0800 (PST)
david@lang.hm wrote:

> On Wed, 17 Feb 2010, Nick Bowler wrote:
> 
> > On 19:27 Wed 17 Feb     , Volker Armin Hemmann wrote:
> >> On Mittwoch 17 Februar 2010, Nick Bowler wrote:
> >>> On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> >>>> for a distro that is trying to make one kernel image run on every
> >>>> possible type of hardware features like initramfs (and udev, modeules,
> >>>> etc) are wonderful.
> >>>>
> >>>> however for people who run systems that are known ahead of time and
> >>>> static (and who build their own kernels instead of just relying on the
> >>>> distro default kernel), all of this is unnessesary complication, which
> >>>> leaves more room for problems to creep in.
> >>>
> >>> Such people can easily construct an initramfs containing busybox and
> >>> mdadm with a shell script hardcoded to mount their root fs and run
> >>> switch_root.  It's a ~10 minute jobbie that only needs to be done once.
> >>
> >> and even better when you don't have to do that one time job at all.
> >
> > But people who are building their own kernels are already doing a
> > (much harder, imo) one time job of configuring their kernels.
> >
> >> btw, what about additional delay?
> >
> > It takes about half a second for mdadm to assemble my root array, is
> > that what you're referring to?
> >
> > I assume that kernel auto-assembly is no faster, although I've never
> > used it.  Regardless, half a second isn't very long to wait.
> 
> If you are aiming for a 5-second boot time it's 10% of your total boot 
> time. That's a lot for a feature that's not needed.

It is worth noting that the Team that was recently working for v.short boot
times wanted to disable in-kernel autodetect for RAID, and added a
compile-time option to do just that.

The reason is that before the in-kernel autodetection can work reliably you
have to wait for all storage devices to have been discovered.  That wait
can unnecessarily increase the total boot time.

Using user-space autodetection, you can plug "mdadm -I" into udev, and have
arrays assembled as they are found, and filesystems mounted as arrays are
assembled, and then you just have to wait for the root filesystem to appear,
not for "all devices".

Yes, you could make the in-kernel autodetection smarter so it doesn't have to
wait quite so long, but that would make it quite a bit more complex, and it
is harder to maintain the complexity in the kernel.

NeilBrown

Re: (boot time consequences of) Linux mdadm superblock question.

[martin f krafft]

[-- Attachment #1: Type: text/plain, Size: 1366 bytes --]

also sprach Neil Brown <neilb@suse.de> [2010.02.18.1224 +1300]:
> Using user-space autodetection, you can plug "mdadm -I" into udev,
> and have arrays assembled as they are found, and filesystems
> mounted as arrays are assembled, and then you just have to wait
> for the root filesystem to appear, not for "all devices".

The mdadm experimental package offers this via debconf (default off
for now). I would appreciate testers — I literally whacked this up
on a rainy Sunday with an hangover, and while it seems to work fine,
it's probably got warts.

If you don't run Debian or a derivative, you can get the files from
debian/initramfs/* in git://git.debian.org/pkg-mdadm/mdadm.git or

  http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=tree;f=debian/initramfs;hb=HEAD

don't be scared off by the complexity, incremental assembly actually
bypasses most of the (shell) code in both scripts.

> Yes, you could make the in-kernel autodetection smarter so it
> doesn't have to wait quite so long, but that would make it quite
> a bit more complex, and it is harder to maintain the complexity in
> the kernel.

It is definitely a user-space task, if you ask me.

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
windows 2000: designed for the internet.
the internet: designed for unix.
 
spamtraps: madduck.bogus@madduck.net

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Re: (boot time consequences of) Linux mdadm superblock question.

[Henrique de Moraes Holschuh]

On Thu, 18 Feb 2010, Neil Brown wrote:
> Using user-space autodetection, you can plug "mdadm -I" into udev, and have
> arrays assembled as they are found, and filesystems mounted as arrays are
> assembled, and then you just have to wait for the root filesystem to appear,
> not for "all devices".

Is this ready for testing somewhere?  initramfs+mdadm.conf is operator-error
bait, proper auto-assemble that does away with the requirement of an
up-to-date mdadm.conf inside the initrd would help a great deal, there.

It will need something like LVM has to blacklist/whitelist what device
classes it will scan for superblocks though, or it will eventually cause a
lot of trouble.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: (boot time consequences of) Linux mdadm superblock question.

[martin f krafft]

[-- Attachment #1: Type: text/plain, Size: 1291 bytes --]

also sprach Henrique de Moraes Holschuh <hmh@hmh.eng.br> [2010.02.18.1558 +1300]:
> > Using user-space autodetection, you can plug "mdadm -I" into
> > udev, and have arrays assembled as they are found, and
> > filesystems mounted as arrays are assembled, and then you just
> > have to wait for the root filesystem to appear, not for "all
> > devices".
> 
> Is this ready for testing somewhere?  initramfs+mdadm.conf is
> operator-error bait, proper auto-assemble that does away with the
> requirement of an up-to-date mdadm.conf inside the initrd would
> help a great deal, there.

Debian experimental. But so far, I was unable to get rid of
mdadm.conf because it only works without the info in that file if
the homehost is correctly encoded in the metadata. So the challenge
I am facing is http://bugs.debian.org/567468.

> It will need something like LVM has to blacklist/whitelist what
> device classes it will scan for superblocks though, or it will
> eventually cause a lot of trouble.

We rely on linux-base reporting the FS type as linux_raid_member and
mdadm -E finding the metadata if that's the case.

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
sex an und für sich ist reine selbstbefriedigung.
 
spamtraps: madduck.bogus@madduck.net

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Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Mittwoch 17 Februar 2010, Nick Bowler wrote:
> On 19:27 Wed 17 Feb     , Volker Armin Hemmann wrote:
> > On Mittwoch 17 Februar 2010, Nick Bowler wrote:
> > > On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> > > > for a distro that is trying to make one kernel image run on every
> > > > possible type of hardware features like initramfs (and udev,
> > > > modeules, etc) are wonderful.
> > > > 
> > > > however for people who run systems that are known ahead of time and
> > > > static (and who build their own kernels instead of just relying on
> > > > the distro default kernel), all of this is unnessesary complication,
> > > > which leaves more room for problems to creep in.
> > > 
> > > Such people can easily construct an initramfs containing busybox and
> > > mdadm with a shell script hardcoded to mount their root fs and run
> > > switch_root.  It's a ~10 minute jobbie that only needs to be done once.
> > 
> > and even better when you don't have to do that one time job at all.
> 
> But people who are building their own kernels are already doing a
> (much harder, imo) one time job of configuring their kernels.
> 
> > btw, what about additional delay?
> 
> It takes about half a second for mdadm to assemble my root array, is
> that what you're referring to?
> 
> I assume that kernel auto-assembly is no faster, although I've never
> used it.  Regardless, half a second isn't very long to wait.

well at the moment it takes less than two seconds until init takes over.

Adding .5 seconds is a lot. And loading the initrd and changing root isn't 
free either, true?

I remember well all the noise in the past about making linux booting faster. 
So why slow it down with an initrd - especially if you can do without?

Glück Auf,
Volker

Re: Linux mdadm superblock question.

[H. Peter Anvin]

On 02/17/2010 10:46 AM, Volker Armin Hemmann wrote:
> 
> well at the moment it takes less than two seconds until init takes over.
> 
> Adding .5 seconds is a lot. And loading the initrd and changing root isn't 
> free either, true?
> 
> I remember well all the noise in the past about making linux booting faster. 
> So why slow it down with an initrd - especially if you can do without?
> 

Note that an extremely lightweight initramfs can quite possibly be
faster than doing it in the kernel, just because userspace is so much
less constrained.  I was hoping klibc would catch on for this stuff, but
it hasn't as much as I'd like.

	-hpa

Re: Linux mdadm superblock question.

[Goswin von Brederlow]

Nick Bowler <nbowler@elliptictech.com> writes:

> On 09:41 Wed 17 Feb     , david@lang.hm wrote:
>> for a distro that is trying to make one kernel image run on every
>> possible type of hardware features like initramfs (and udev, modeules,
>> etc) are wonderful.
>> 
>> however for people who run systems that are known ahead of time and
>> static (and who build their own kernels instead of just relying on the
>> distro default kernel), all of this is unnessesary complication, which
>> leaves more room for problems to creep in.
>
> Such people can easily construct an initramfs containing busybox and
> mdadm with a shell script hardcoded to mount their root fs and run
> switch_root.  It's a ~10 minute jobbie that only needs to be done once.

Except when mdadm, cryptsetup, lvm change you need to update it.
Esspecially when you set up a new system that might have newer
metadata.

Also at least Debian doesn't (yet) support a common initramfs for their
kernel packaging. You either build a kernel without need for one or you
have a per kernel initramfs that is automatically build and updated
whenever anything in the initrmafs changes. Not often, but still too
often, the initramfs then doesn't work.

Does any other distribution allow building kernel image rpms that will
use a common initramfs for all kernels?

MfG
        Goswin

Re: Linux mdadm superblock question.

[Nick Bowler]

On 04:33 Thu 18 Feb     , Goswin von Brederlow wrote:
> Nick Bowler <nbowler@elliptictech.com> writes:
> 
> > On 09:41 Wed 17 Feb     , david@lang.hm wrote:
> >> however for people who run systems that are known ahead of time and
> >> static (and who build their own kernels instead of just relying on the
> >> distro default kernel), all of this is unnessesary complication, which
> >> leaves more room for problems to creep in.
> >
> > Such people can easily construct an initramfs containing busybox and
> > mdadm with a shell script hardcoded to mount their root fs and run
> > switch_root.  It's a ~10 minute jobbie that only needs to be done once.
> 
> Except when mdadm, cryptsetup, lvm change you need to update it.
> Esspecially when you set up a new system that might have newer
> metadata.

I meant "once per system".  One typically doesn't _need_ to update the
mdadm in the initramfs, as long as it's capable of assembling the root
array.

> Also at least Debian doesn't (yet) support a common initramfs for their
> kernel packaging. You either build a kernel without need for one or you
> have a per kernel initramfs that is automatically build and updated
> whenever anything in the initrmafs changes. Not often, but still too
> often, the initramfs then doesn't work.

The scenario was when users configure and build their own kernel.  These
users are presumably capable of using grub's "initrd" command or the
CONFIG_INITRAMFS_SOURCE kernel option.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

Re: Linux mdadm superblock question.

[Michael Evans]

I actually much prefer building my own kernel for servers and
higher-end workstations.  I like having all the core drivers needed to
'get running' in there; even if the more delicate but static logic of
how to track down and assemble/unlock the drives is in the initramfs
image.

The only really annoying issue I've had with my custom initramfs
creator is getting it 'chained' by various distros auto-initramfs
update triggers so that it can grab the version of modules that match
a given kernel.  I have several ways in mind to work around that issue
at various steps, but no known userbase to support besides my self and
thus less motivation to work on that task.

Everything else of course works exactly the same as long as the
configuration hasn't changed on the host system.

Re: Linux mdadm superblock question.

[Henrique de Moraes Holschuh]

On Sat, 13 Feb 2010, Michael Evans wrote:
> I remember hearing that 1.x had /no/ plans for kernel level
> auto-detection ever.  That can be accomplished in early-userspace
> leaving the code in the kernel much less complex, and therefore far
> more reliable.

Yes, it is far more reliable kernel side, if only because it doesn't do
anything.

But the userspace reliability is _not_ good.  initrds are a source of
problems the moment things start to go wrong, and that's when they are not
the problem themselves.

And the end result is a system that needs manual intervention to get its
root filesystem back.

In my experience, every time we moved critical codepaths to userspace, we
ended up decreasing the *overall* system reliability.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: Linux mdadm superblock question.

[Michael Evans]

On Sun, Feb 14, 2010 at 11:34 AM, Henrique de Moraes Holschuh
<hmh@hmh.eng.br> wrote:
> On Sat, 13 Feb 2010, Michael Evans wrote:
>> I remember hearing that 1.x had /no/ plans for kernel level
>> auto-detection ever.  That can be accomplished in early-userspace
>> leaving the code in the kernel much less complex, and therefore far
>> more reliable.
>
> Yes, it is far more reliable kernel side, if only because it doesn't do
> anything.
>
> But the userspace reliability is _not_ good.  initrds are a source of
> problems the moment things start to go wrong, and that's when they are not
> the problem themselves.
>
> And the end result is a system that needs manual intervention to get its
> root filesystem back.
>
> In my experience, every time we moved critical codepaths to userspace, we
> ended up decreasing the *overall* system reliability.
>
> --
>  "One disk to rule them all, One disk to find them. One disk to bring
>  them all and in the darkness grind them. In the Land of Redmond
>  where the shadows lie." -- The Silicon Valley Tarot
>  Henrique Holschuh
>

Maybe you'd like a simple, easy to customize initramfs creator.
That's exactly what I was aiming for when I made AEUIO
https://sourceforge.net/projects/aeuio  There are some things that
could use improvement, but if your system can boot without loading
modules it should be more than sufficient even across kernel versions.

Re: Linux mdadm superblock question.

[Henrique de Moraes Holschuh]

On Sun, 14 Feb 2010, Michael Evans wrote:
> Maybe you'd like a simple, easy to customize initramfs creator.

If the distro doesn't use it (as its default initramfs creator, even), it is
a lot more chance for breakage.  Less testing, and all that...

And if I am deploying a specific kernel in a server, you better believe it
is important enough that all due care will be taken so that it won't need an
initrd to mount the root filesystem to begin with ;-)

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: Linux mdadm superblock question.

[Asdo]

Henrique de Moraes Holschuh wrote:
> On Sat, 13 Feb 2010, Michael Evans wrote:
>   
>> I remember hearing that 1.x had /no/ plans for kernel level
>> auto-detection ever.  That can be accomplished in early-userspace
>> leaving the code in the kernel much less complex, and therefore far
>> more reliable.
>>     
>
> Yes, it is far more reliable kernel side, if only because it doesn't do
> anything.
>
> But the userspace reliability is _not_ good.  initrds are a source of
> problems the moment things start to go wrong, and that's when they are not
> the problem themselves.
>
> And the end result is a system that needs manual intervention to get its
> root filesystem back.
>
> In my experience, every time we moved critical codepaths to userspace, we
> ended up decreasing the *overall* system reliability.
>   
I don't see it like this.
You have the same chance to screw up the system by making mistakes in 
the files in /etc, in the networking config, the firewall, the server 
applications...
(note: I speak for Debian/Ubuntu, redhat's initramfs I think is more messy.)
1.x autodetection worked great for me in initramfs. Basically you only 
need /etc/mdadm/mdadm.conf copied to initramfs (via update-initramfs), 
the rest is done by Debian/Ubuntu standard initramfs procedure.
Also consider 1.x allows to choose which arrays are autoassembled 
(hostname written in the array name equal to hostname in the machine or 
specified in mdadm.conf): this is more precise than 0.9 which 
autoassembles all, I think.

Re: Linux mdadm superblock question.

[Henrique de Moraes Holschuh]

On Sun, 14 Feb 2010, Asdo wrote:
> >In my experience, every time we moved critical codepaths to userspace, we
> >ended up decreasing the *overall* system reliability.
> I don't see it like this.
> You have the same chance to screw up the system by making mistakes
> in the files in /etc, in the networking config, the firewall, the
> server applications...

Those don't require a reboot test to verify, and are far easier to rollback.

Also, they can (and SHOULD) be done on testbeds.  While the kind of screwup
where an initramfs decides to bite you hard, usually cannot (they tend to
happen when things already went horribly wrong).

> (note: I speak for Debian/Ubuntu, redhat's initramfs I think is more messy.)
> 1.x autodetection worked great for me in initramfs. Basically you
> only need /etc/mdadm/mdadm.conf copied to initramfs (via
> update-initramfs), the rest is done by Debian/Ubuntu standard
> initramfs procedure.

Yeah, cute.  What happens when the initrd is not updated for whatever
reason?  That is a new failure mode that doesn't exist with 0.9 and kernel
autorun.

It boils down to whether failure modes new to 1.x without autorun are more
likely to happen than the failure modes that are specific to 0.9 with
autorun.

IME, the 0.9 ones are less likely to happen, and I have been through quite a
few incidents involving boot problems.  Experience told me that initrds are
far more prone to operator errors than the kernel autorun.  Debian's
*stable* initramfs creators have not screwed up on me yet, but I am well
aware that they could.

> Also consider 1.x allows to choose which arrays are autoassembled
> (hostname written in the array name equal to hostname in the machine
> or specified in mdadm.conf): this is more precise than 0.9 which
> autoassembles all, I think.

That can be either a good or bad thing depending on the situation, so I
would never use it to count for (or against) 1.x or 0.9.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: Linux mdadm superblock question.

[Gabor Gombas]

On Sun, Feb 14, 2010 at 09:47:16PM +0100, Asdo wrote:

> 1.x autodetection worked great for me in initramfs. Basically you
> only need /etc/mdadm/mdadm.conf copied to initramfs (via
> update-initramfs),

There is no autodetection with 1.1. Once you have mdadm.conf you have
pretty hard rules about what to look for and how to assemble it - ie.
there is not much left to "auto" detect. Real autodetection would mean
there is _no_ such information available, and you figure out everything
by just looking at the devices you find.

> initramfs procedure.
> Also consider 1.x allows to choose which arrays are autoassembled
> (hostname written in the array name equal to hostname in the machine
> or specified in mdadm.conf): this is more precise than 0.9 which
> autoassembles all, I think.

And also causes much more pain when you install machines on an internal
network where it gets a random name (in fact all new machines get the
same temporary name), then it is moved to its real location and
reconfigured with its real name. And you wonder why your arrays aren't
assembled any more...

Gabor

Re: Linux mdadm superblock question.

[martin f krafft]

[-- Attachment #1: Type: text/plain, Size: 870 bytes --]

also sprach Gabor Gombas <gombasg@digikabel.hu> [2010.02.15.1028 +1300]:
> There is no autodetection with 1.1. Once you have mdadm.conf you have
> pretty hard rules about what to look for and how to assemble it - ie.
> there is not much left to "auto" detect. Real autodetection would mean
> there is _no_ such information available, and you figure out everything
> by just looking at the devices you find.

Which, coincidentally, is where we're heading with incremental
assembly. Check the Debian experimental package if you want to try.

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
"we should have a volleyballocracy.
 we elect a six-pack of presidents.
 each one serves until they screw up,
 at which point they rotate."
                                                      -- dennis miller
 
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Re: Linux mdadm superblock question.

[Volker Armin Hemmann]

On Dienstag 16 Februar 2010, John Robinson wrote:
> On 14/02/2010 19:13, Volker Armin Hemmann wrote:
> > On Sonntag 14 Februar 2010, you wrote:
> >> On 14/02/2010 18:40, Volker Armin Hemmann wrote:
> >>> On Sonntag 14 Februar 2010, you wrote:
> >>>> In other words, 'auto-detection' for 1.x format devices is using an
> >>>> initrd/initramfs.
> >>> 
> >>> which makes 1.x format useless for everybody who does not want to deal
> >>> with initrd/initramfs.
> >> 
> >> True, but afaik every distro uses an initrd/initramfs and bundles tools
> >> making it easy to manage and customise them, so what's the problem?
> > 
> > and distros do it because of all the drivers they have to ship. But for
> > example I am not bound by such limitations. Why should I deal with that?
> > It is hard enough not to forget 'make modules_install'. And now add
> > initrd. Autodetecting just works - but if you use an initrd an it
> > doesn't. Where do you start?
> > 
> > Initrd's maybe great for distro packagers, but are they really usefull
> > for anybody else?
> 
> Not just for distro packagers, they're useful for distro users, which
> are presumably 99% of Linux users these days, including the vast
> majority of enterprise users who like tested, supported systems.
> 
> But even for people building their own kernels, initrd/initramfs are
> useful if you're using LVM, or indeed trying to boot off anything that's
> not a simple device.

so assume you have an initrd and metadata 1.x without auto assembling.

You do some changes to the raid and screw up something else. Next boot nothing 
works. Mostly because the mdadm.conf in your initrd is not correct.

You whip out your trusty usb stick with a resuce system - and you are stuck. 
If autoassembling would work, you would have working md devices you could 
mount and edit the files you have to. But you don't and the mdadm.conf in the 
initrd is outdated.

Sounds like 'you are screwed'.

Or you have that famous grub boot line to have root autoassembled but the 
device names changed. 

Yeah, sounds really great.

And that because ...? Is there any good reason not to have autoassmbling in 
the kernel?

Glück Auf
Volker

Re: Linux mdadm superblock question.

[John Robinson]

On 16/02/2010 14:37, Volker Armin Hemmann wrote:
> On Dienstag 16 Februar 2010, John Robinson wrote:
>> On 14/02/2010 19:13, Volker Armin Hemmann wrote:
>>> On Sonntag 14 Februar 2010, you wrote:
>>>> On 14/02/2010 18:40, Volker Armin Hemmann wrote:
>>>>> On Sonntag 14 Februar 2010, you wrote:
>>>>>> In other words, 'auto-detection' for 1.x format devices is using an
>>>>>> initrd/initramfs.
>>>>> which makes 1.x format useless for everybody who does not want to deal
>>>>> with initrd/initramfs.
>>>> True, but afaik every distro uses an initrd/initramfs and bundles tools
>>>> making it easy to manage and customise them, so what's the problem?
>>> and distros do it because of all the drivers they have to ship. But for
>>> example I am not bound by such limitations. Why should I deal with that?
>>> It is hard enough not to forget 'make modules_install'. And now add
>>> initrd. Autodetecting just works - but if you use an initrd an it
>>> doesn't. Where do you start?
>>>
>>> Initrd's maybe great for distro packagers, but are they really usefull
>>> for anybody else?
>> Not just for distro packagers, they're useful for distro users, which
>> are presumably 99% of Linux users these days, including the vast
>> majority of enterprise users who like tested, supported systems.
>>
>> But even for people building their own kernels, initrd/initramfs are
>> useful if you're using LVM, or indeed trying to boot off anything that's
>> not a simple device.
> 
> so assume you have an initrd and metadata 1.x without auto assembling.
> 
> You do some changes to the raid and screw up something else. Next boot nothing 
> works. Mostly because the mdadm.conf in your initrd is not correct.
> 
> You whip out your trusty usb stick with a resuce system - and you are stuck. 
> If autoassembling would work, you would have working md devices you could 
> mount and edit the files you have to. But you don't and the mdadm.conf in the 
> initrd is outdated.
> 
> Sounds like 'you are screwed'.

No; mdadm can assemble arrays without needing a conf file (at least 
arrays which have superblocks).

And if you have otherwise screwed something up with the RAID, no amount 
of in-kernel autoassembly is going to help, in fact it's more likely to 
get it wrong and make things worse; you need a command line and mdadm to 
sort it out.

Cheers,

John.