Very bad FreeBSD SCSI RAID5 write speed performance

[Martin Blapp]

Hi all,

We are currently testing some raid configurations with Linux
and FreeBSD.

It seems that FreeBSD does something wrong. An adaptec 3200S
controller and a IBM ServeRaid5i controller are both times slower
with RAID5 on FreeBSD as they are on linux.

Both controllers are batterie-backed, have cacheing enabled.

Does anyone with these controllers (drivers) can take some
numbers of the write-performance ?

If needed I can provide numbers (taken with iozone). I've tested it
on a async mounted filesystem on both FreeBSD and Linux. And it is not
only a benchmark problem. We suffer on this problem on production
machines. The production machines perform a bit better since they
run 4.X, but still bad (Linux is 3,5 times faster), on CURRENT Linux
is 4 times faster.

Martin

Martin Blapp, <mb at imp.ch> <mbr at FreeBSD.org>
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