Extremely slow write speeds to disk : FreeBSD 7.1 and Dell

John LLOYD jal at mdacorporation.com
Tue Feb 10 11:45:22 CST 2009


> I have attempted most of the popular BSD Variants such as NetBSD, Open
> BSD, FreeBSD...
> The only distrubution that seems to work on the is Dell SAS 
> 6/iR Adapter
> is FreeBSD 7.1
> Firmware version & date : 9/29/2008	00.25.47.00
> 
> But the issue is that writing to disk is extremely 
> slow...i.e. 14Mb per
> second....

As usual, there are a lot of things which have to work together.  I
would recommend using bonnie++ for performance testing; as tests with dd
can vary quite a lot depending on options you choose.  

For OpenBSD, use a recent release (4.3 or 4.4).  You can try turning off
ACPI, 

   UKC> disable acpi

as the ACPI mechanism which distributes the interrupt load of
controllers across various IRQs could be wrong. Use vmstat -fiz to
review the irq distribution and allocation.  For OpenBSD, the mfi driver
talks to PERC controllers. 

Check the RAID controller is not performing a rebuild while you boot or
install.  The I/O performance you see may be due to competition with
this I/O load.  (I'm not aware of a method in OBSD to test for this, you
probably have to check at the BIOS level.)

Compare the speed of a raw disk (no raid, or a RAID-1 set consisting of
just one disk) to verify it is not some bad disk drive doing things to
your performance.

You might also want to compare release notes from Dell for various
firmware releases for perc5/perc6 controllers.  On an R900 I saw a
tremendous increase in performance on a perc6/e with an upgrade in
firmware, but there were some compatibility issues for a similar release
on a perc5/e which we could not use.  Worst case, you could try a
downgrade of the firmware.



--John



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