RHEL3 and SAS5/iR: very bad performance

Eric Rostetter rostetter at mail.utexas.edu
Wed Jan 24 08:54:00 CST 2007

Quoting Giulio Orsero <giulioo at gmail.com>:

> Case #1 (simple SATA disk):
> - bonnie (file=RAMx2): about 70MB/s writes, about 80MB/s reads
> Case #2 (SAS5/iR DRV 2.06.32 FW- BIOS-
> - bonnie (file=RAMx2): about 40MB/s writes, about 120MB/s reads

This isn't bad.  RAID-1 will have slower writes (since it has to
write twice), but faster reads (since it can do two reads at once)
which is what you are seeing.

So the performance of the disk setups seems fine as far as the
bonnie test shows.

> Case #1 (simple SATA disk):
> - custom database app (write data):
> 	job1 = 5 mins
> 	job2 = 20 mins
> Case #2 (SAS5/iR DRV 2.06.32 FW- BIOS-
> - bonnie (file=RAMx2): about 40MB/s writes, about 120MB/s reads
> - custom database app (write data):
> 	job1 = 15 mins
> 	job2 =  4/5 hours  (yes hours instead of 20mins, this is db rebuilding
> indexes)

This implies some problem with the application code or with system tuning.
If bonnie gets correct results, but the application doesn't, then the
application needs to be tuned, or the system needs to be tuned for the
application, or the application needs a different disk setup.

> Is there some magical module parameters (mptbase or mptscsih) or compile
> time switch to give SAS5/iR some decent performance in writes?
> I can't believe this is normal behavior.

There are several possibilities (raid card settings, filesystem settings,
application tuning, etc).  No one magic answer for all cases.

> If possible don't tell me to switch to PERC5 :-)

Probably wouldn't help (but would be interesting to see though).

> Before buying many SAS5/iR, Dell tech person assured me performance in RAID1
> is basically the same on SAS5/iR and PERC5 as far as hardware is concerned.

I'd guess the same, though I have no data to support it.

> Thanks
> --
> giulioo at pobox.com

Eric Rostetter
The Department of Physics
The University of Texas at Austin

Go Longhorns!

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