Very bad FreeBSD SCSI RAID5 write speed performance

[Gary Stanley]

Well.

W/O softupdates

root at 64:[/tmp/blah]>dd if=/dev/zero of=/tmp/blah/blah
89472+0 records in
89471+0 records out
45809152 bytes transferred in 8.546312 secs (5360108 bytes/sec)

W/ Softupdates
root at 64:[/mnt]>dd if=/dev/zero of=/mnt/blah
116160+0 records in
116159+0 records out
59473408 bytes transferred in 10.080428 secs (5899889 bytes/sec)

Just about the same. But this machine's write caching settings for the 
controller (LSI MegaRaid) are not correct for Raid 5, and the machine's 
under some moderate load, so when I get a chance to correct them I'll 
repost my findings. I always seem to suffer heavy write speed losses w/ 
Raid5, but I can't complain because the read speeds make up for it.

Also, I use U320 Maxtor Atlas 10K drives, MegaRaid (Latest Firmware, broken 
Cache Settings)





At 05:33 AM 11/13/2003, you wrote:

>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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