How does RAID work with IT8212 RAID PCI card?

How does RAID work with IT8212 RAID PCI card?

[Christian Härtwig]

Hello everybody,

i need some advise regarding the usage of the above kernel module. Today i 
have plugged a PCI RAID card into my computer, IT8212 chip on it, and two 
identical hard drives on the primary and secondary master of that controller. 
In the controller BIOS i defined a mirror set out of those both disks and 
booted linux afterwards.

Loading the kernel module dmesg showed that the controller was found and that 
2 harddiscs are attached to it.

The thing that i wonder about is, that i still can "see" both harddisks 
independently, but i would expect to see only one harddisk at all, that 
represents the RAID set. Udev also registers /dev/hde and /dev/hdg, but (as 
far as i can see) no further device.

Is there anything wrong about my setup? Is this i driver issue? Or is this the 
normal and expected behaviour and its me who doesn't "use" the module 
properly? How to i access the RAID set instead of the two seperate disks?

Thanks in advance. Yours sincerely,
Christian Haertwig

Re: How does RAID work with IT8212 RAID PCI card?

[Lennart Sorensen]

On Tue, Jun 13, 2006 at 05:58:45PM +0200, Christian H?rtwig wrote:
> i need some advise regarding the usage of the above kernel module. Today i 
> have plugged a PCI RAID card into my computer, IT8212 chip on it, and two 
> identical hard drives on the primary and secondary master of that controller. 
> In the controller BIOS i defined a mirror set out of those both disks and 
> booted linux afterwards.
> 
> Loading the kernel module dmesg showed that the controller was found and that 
> 2 harddiscs are attached to it.
> 
> The thing that i wonder about is, that i still can "see" both harddisks 
> independently, but i would expect to see only one harddisk at all, that 
> represents the RAID set. Udev also registers /dev/hde and /dev/hdg, but (as 
> far as i can see) no further device.
> 
> Is there anything wrong about my setup? Is this i driver issue? Or is this the 
> normal and expected behaviour and its me who doesn't "use" the module 
> properly? How to i access the RAID set instead of the two seperate disks?

Congratulations.  You have a fake raid card by the sound of it.  A
hardware raid card would have only shown one drive, while a fake raid
card expects the driver to work with the bios to find out the setup (and
handle booting), and then the driver does all the raid work in software.

It is much simpler to treat fake raid cards as just another drive
controller and use linux software raid on it.  At least then you know
how it works, and it is portable to other controllers later if needed.

Len Sorensen

Re: How does RAID work with IT8212 RAID PCI card?

[Matheus Izvekov]

On 6/13/06, Lennart Sorensen <lsorense@csclub.uwaterloo.ca> wrote:
> On Tue, Jun 13, 2006 at 05:58:45PM +0200, Christian H?rtwig wrote:
> > i need some advise regarding the usage of the above kernel module. Today i
> > have plugged a PCI RAID card into my computer, IT8212 chip on it, and two
> > identical hard drives on the primary and secondary master of that controller.
> > In the controller BIOS i defined a mirror set out of those both disks and
> > booted linux afterwards.
> >
> > Loading the kernel module dmesg showed that the controller was found and that
> > 2 harddiscs are attached to it.
> >
> > The thing that i wonder about is, that i still can "see" both harddisks
> > independently, but i would expect to see only one harddisk at all, that
> > represents the RAID set. Udev also registers /dev/hde and /dev/hdg, but (as
> > far as i can see) no further device.
> >
> > Is there anything wrong about my setup? Is this i driver issue? Or is this the
> > normal and expected behaviour and its me who doesn't "use" the module
> > properly? How to i access the RAID set instead of the two seperate disks?
>
> Congratulations.  You have a fake raid card by the sound of it.  A
> hardware raid card would have only shown one drive, while a fake raid
> card expects the driver to work with the bios to find out the setup (and
> handle booting), and then the driver does all the raid work in software.
>
> It is much simpler to treat fake raid cards as just another drive
> controller and use linux software raid on it.  At least then you know
> how it works, and it is portable to other controllers later if needed.
>
> Len Sorensen
> -

No not true, i have this card and its a true hardware raid card. The
thing is, this card has both a raid and a passthru mode, you should
check which bios is flashed into it. Google is your friend.

Re: How does RAID work with IT8212 RAID PCI card?

[Lennart Sorensen]

On Tue, Jun 13, 2006 at 01:20:55PM -0300, Matheus Izvekov wrote:
> No not true, i have this card and its a true hardware raid card. The
> thing is, this card has both a raid and a passthru mode, you should
> check which bios is flashed into it. Google is your friend.

Hmm, you would think that if the bios lets you setup a raid, then it
must have raid mode enabled then.  Or does it need a different driver to
work then?

Len Sorensen

Re: How does RAID work with IT8212 RAID PCI card?

[Matheus Izvekov]

On 6/13/06, Lennart Sorensen <lsorense@csclub.uwaterloo.ca> wrote:
> On Tue, Jun 13, 2006 at 01:20:55PM -0300, Matheus Izvekov wrote:
> > No not true, i have this card and its a true hardware raid card. The
> > thing is, this card has both a raid and a passthru mode, you should
> > check which bios is flashed into it. Google is your friend.
>
> Hmm, you would think that if the bios lets you setup a raid, then it
> must have raid mode enabled then.  Or does it need a different driver to
> work then?
>
> Len Sorensen
>

Im not sre, never flashed the bios for passthru mode, because the
driver lets you select the mode thru some modparm. But maybe the
different bios only changes the default mode.
Anyway, this card is hardware raid for sure.

Re: How does RAID work with IT8212 RAID PCI card?

[Alan Cox]

Ar Maw, 2006-06-13 am 12:01 -0400, ysgrifennodd Lennart Sorensen:
> Congratulations.  You have a fake raid card by the sound of it.  A
> hardware raid card would have only shown one drive, while a fake raid
> card expects the driver to work with the bios to find out the setup (and
> handle booting), and then the driver does all the raid work in software.

The IT8212 is not a fake raid card - it depends on the firmware whether
you see a drive per raid volume (hardware raid mode) or not (ATAPI
capable firmware). We've found the raid firmware seems quite
temperamental and there is little performance gain from raid 1 in
hardware over software so using md or device mapper is recommended for
that reason.