Dell/Perc5 raid/MPT SAS Integrated Raid Write Performance
mjacob at freebsd.org
mjacob at freebsd.org
Fri May 18 23:31:04 UTC 2007
A lot of users have seen some very poor write performance on the MPT
(LSI-Logic) driven SAS/SATA controllers, particularly those that
function in Integrated Raid (mirroring) mode.
Some of the reported performance issues are pretty clearly single
spindle small transfer IOPS issues. For example, directory intensive and
small file operations like mail server applications can do very poorly
on single spindle SATA drives that are connected via a SAS channel that
doesn't enable write cacheing on the SATA drive (i.e., does not flow
through WCE for SCSI emulation, as the LSI-Logic *apparently* does not).
Benchmarks like Postmark show pretty amazing differences when run on a
PATA or native SATA based drive (1000s of ops/second) and on single
Fibre Channel or SCSI drives (100s of ops/second) and can be even worse
for SATA drives on a SAS controller.
In these cases, there isn't much to be done- the h/w being picked
doesn't match the application.
However, other users have reported things which are *clearly* bad
performance issues. In these cases users have reported sequential write
speed to be a small fraction of read speed. That is, a single threaded
read of a 10GB file will get spindle rotational speed magnitude for the
disk in question (~40MB/s) but will only write at around ~6MB/s. This is
clearly broken and wrong.
Since I don't actually have a *lot* of MPT h/w and none that shows this
write performance problem could folks do me a favor and at the next
reboot get into the LSI-Logic BIOS utilities and find me all the
firmware revision numbers? This might help me nail down some differences
to go talk to LSI-Logic about.
The overriding LSI-Logic BIOS revision is of interest, but also any of
the firmware revision numbers. For example, the loaned Sunfire 4100 I
have has 18.104.22.168 for the BIOS revision, but 1.04.00.00-IR for the
firmware- and this system, which has two integral SAS 2.5" drives,
writes at 50MB/s with them set up as an integrated mirror.
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