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* Re: [reiserfs-list] ReiserFS on RAID5 Linux-2.4 - speed problem
       [not found] ` <20011129022247.43615e45.rene.rebe@gmx.net>
@ 2001-11-29 17:11 Edward Shushkin
       [not found] ` <20011129022247.43615e45.rene.rebe@gmx.net>
  0 siblings, 1 reply; 5+ messages in thread
From: Edward Shushkin @ 2001-11-29 17:11 UTC (permalink / raw)
  To: Rene Rebe; +Cc: linux-kernel, reiserfs-list

Rene Rebe wrote:
> 
> (Repost - since my first mail has still not arrived ...)
> 
> Hi - I need some speed tips for using ReiserFS on an RAID5 Linux-soft-raid device.
> 
> Config: AMD K6-2 350
>         3x IBM 40GB IDE discs (connected as master each to a single IDE channel)
>         Linux-2.4.1x (currently .16)
>         the discs are combined via Linux-software-RAID5
> 
> I run ReiserFS on a RAID5 (of 3 IDE disks) using the latest 2.4.(e.g.16)
> kernel for weeks. It works well except that is is painfully slow. In todays tests
> I got arround 3MB/s from ReiserFS (dd if=/home/database/some-video.avi ...) - wich
> matches exatly what I get over NFS for normal development usage, too. The IDE or
> RAID setup doesn't seem to be a problem because I get 33MB/s when I read the
> /dev/md/0 directly (dd if=/dev/md/0 ...)!

Thats odd!
I don't have three various ide-controllers to reproduce your configuration, 
but for the raid5 of 3 various scsi disks i have that the times of dd readings for 
if= /dev/sda, /dev/md0, /mnt/file_on_reiserfs_on_md0 relates approximately as 
1.5 : 1 : 1   
So the performance doesn't decrease..
What is about your speed for (dd if=/dev/hdx...)??
Can you measure this for ext2 on md0?

Thanks,
Edward.

^ permalink raw reply	[flat|nested] 5+ messages in thread
* RE: [reiserfs-list] ReiserFS on RAID5 Linux-2.4 - speed problem
@ 2001-11-29 21:36 Torrey Hoffman
  2001-11-29 22:55 ` Rene Rebe
  0 siblings, 1 reply; 5+ messages in thread
From: Torrey Hoffman @ 2001-11-29 21:36 UTC (permalink / raw)
  To: 'Rene Rebe', linux-kernel; +Cc: reiserfs-list

René Rebe wrote:
[...]
> I run ReiserFS on a RAID5 (of 3 IDE disks) using the latest 
> 2.4.(e.g.16)
> kernel for weeks. It works well except that is is painfully 
> slow. 
[...]

You are not the only one with these problems...

I am convinced there is a serious, negative performance 
interaction between software RAID 5 and ReiserFS, at least
on IDE.  Performance is less than 25% of what it should be.

---------------
Concise summary: 

dbench of reiserfs on a normal drive partition is slightly
* faster * than timing a raw "dd" from that partition.

But, dbench of reiserfs on a reiserfs on software RAID5
is ** only 1/4 as fast ** as a raw "dd" from the RAID5, 

And, to make it worse, software RAID 5 is significantly 
slower than I think it should be.  As a result, my nice
RAID 5 is far, far slower than an ordinary partition.
These are not just dbench numbers - all sorts of testing
shows the problem.

---------------
Here are the details:

I have four Maxtor 60 GB IDE disks, each is master on a single
cable, using two Promise Ultra TX2/100 cards.  The host is 
a dual P3-800 with 512 MB of RAM.  I bought this hardware
specifically to act as a fast, cheap, reliable server...  
I have no complaints except the speed.  

The raid disks are hde, hdg, hdi, hdk, as /dev/md0, not
partitioned, /dev/md0 is a single 180 GB reiserfs and is 
mounted on /home.  Chunk size is 1024.

Here's some low level numbers:

Single drive from the RAID:
time dd if=/dev/hdg of=/dev/null bs=1M count=1024
- elapsed time 0:37 = 27.65 MB/sec

Raw RAID5:
time dd if=/dev/md0 of=/dev/null bs=1M count=1024
- elapsed time 0:25 = 40.96 MB/sec

File on Reiserfs on RAID5:
time dd if=/home/test_file_1GB of=/dev/null bs=1M count=1024
- elapsed time 0:33 = 31.03 MB/sec

Old home partition on hda9:
time dd if=/dev/hda9 of=/dev/null bs=1M count=1024
- elapsed time 0:41 = 24 MB/sec

dbench tests:

dbench 32 on reiserfs on md0  : 10.7027 MB/sec
dbench 32 on reiserfs on hda9 : 27.7925 MB/sec

Note that when I first set this hardware up, I tried RAID0
on the same hardware and saw dbench 32 numbers of 76 MB/sec.

So, I think the dbench number for reiserfs on md0 should be
** at least ** five times faster than it is.  Are my 
expectations too high or is there a real problem here?

(tested on 2.4.15-pre5, this problem has been around for
all 2.4 kernels I've tried.)

Happy to help test and debug... please send suggestions.

Torrey Hoffman

^ permalink raw reply	[flat|nested] 5+ messages in thread
* RE: [reiserfs-list] ReiserFS on RAID5 Linux-2.4 - speed problem
@ 2001-11-29 23:36 Torrey Hoffman
  0 siblings, 0 replies; 5+ messages in thread
From: Torrey Hoffman @ 2001-11-29 23:36 UTC (permalink / raw)
  To: 'Rene Rebe'; +Cc: linux-kernel, reiserfs-list

René Rebe wrote:
> Have you tryed:
> 
> echo 1023 > /proc/sys/vm/max-readahead
[...]

Well, I gave that a try.  

note:
/dev/md0 is a 180 GB reiserfs on software RAID 5.
/dev/hda9 is an 18 GB reiserfs on a normal partition.
System is a dual PIII-800 with 512 MB RAM.
Kernel is 2.4.16 + Andrew Morton's Low Latency and I/O 
scheduling patches.

before:
cat /proc/sys/vm/max-readahead:	31
dbench 32 on /dev/md0  :	8.11 MB/sec
dbench 32 on /dev/hda9 :	24.85 MB/sec

after:
echo 1023 > /proc/sys/vm/max-readahead
dbench 32 on /dev/md0  :	8.047 MB/sec
dbench 32 on /dev/hda9 :	24.65 MB/sec

So that change actually made things a little worse,
at least on this kernel.  :-(

Torrey

^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2001-11-29 23:37 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2001-11-29 17:11 [reiserfs-list] ReiserFS on RAID5 Linux-2.4 - speed problem Edward Shushkin
     [not found] ` <20011129022247.43615e45.rene.rebe@gmx.net>
2001-11-29 16:02   ` Rene Rebe
2001-11-29 21:36 Torrey Hoffman
2001-11-29 22:55 ` Rene Rebe
2001-11-29 23:36 Torrey Hoffman

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