Re: Awful Raid10,f2 performance

[Tomasz Chmielewski <mangoo@wpkg.org>]

Jon Nelson schrieb:
> I have set up a 3-disk raid10 using f2 layout using 3x SATA disks each
> capable of 70+ MB/s (give or take).
> The CPU is a dual core 64 bit Athlon 3600+, and the SATA interface
> consists of NVidia MCP55+ (PCIe or whatever).
> Previously this was a 3 disk raid5.
> The problem: I'm getting really awful transfer rates.  7-9MB/s
> per-drive with 21-30MB/s combined. The average hangs around 22-24MB/s.
> This, I feel, is really awful!
> 
> What parameters can I twiddle to improve the performance?
> I am not using NCQ.
> The drives individually are capable of 70+ MB/s.
> I am using the deadline I/O scheduler but I have tried the others.
> This is the openSUSE 2.6.22.17 kernel.
> I am getting the I/O rates via dstat.
> I am using the jfs filesystem primarily.
> The operation I am performing varies but the I/O rates don't (much).
> In particular, moving one 17G file from a logical volume (I am using
> LVM) to another, both filesytems are JFS.
> The load is around 2.6, with these four processing being the top CPU
> consumers (they wiggle around a bit):
> 
> 
>  2034 root      10  -5     0    0    0 D   10  0.0 201:00.30 md0_raid10
> 10631 root      18   0  8436 1076  668 D    7  0.1   2:07.65 mv
>   218 root      15   0     0    0    0 D    3  0.0   2:06.30 pdflush
>  2182 root      10  -5     0    0    0 S    3  0.0   0:32.51 jfsCommit
> 
> Is there more information that I can provide that can help explain why
> I'm getting such slow speeds?

It would be interesting to know the raw values of your RAID-10 (without 
any filesystem).

I.e.

# dd if=/dev/zero of=/dev/md10 bs=64k count=10000
# echo 3 > /proc/sys/vm/drop_caches
# dd if=/dev/md10 of=/dev/null bs=64k


-- 
Tomasz Chmielewski
http://wpkg.org