2120S poor performance

[Bill Anderson]

I've got a 3x72g RAID5 array with U320 disks on an Adaptec 2120S
controller under Freebsd 4.10.  I'm getting about 25MB/s for sequential
reads/writes (e.g.  dd if=/dev/aacd0s1b of=/dev/null bs=32k).  I've
turned on write caching for the container (container set cache
/write_cache_enable) and turned off the read caching, per previous posts
to this list.  I'm going to try setting hw.aac.iosize_max to 96k tonight
to see if that helps.  I'm currently using an IDE disk that gets about
45MB/s, so I can hardly consider it an "upgrade" to switch to a 25MB/s
U320 SCSI system.  :/

I've also read that the 2120S is slow because of its design.  I'm trying
to figure out whether the performance can be increased significantly (I
saw a posting of a linux user getting 37.5MB/s, which although still slow
might be acceptable), or if I'm better off getting a new card.  I'm
thinking the latter is the case based on previous postings, but since it
will probably be quite expensive to replace it, I wanted to get some more
data.

What performance should I be expecting from a decent U320 RAID5
controller?

Has anyone gotten a 2120S to perform above 30Mb/s in FreeBSD?

What's the cheapest controller that still gives reasonable performance?
(If you could give a couple different ones, with their associated
performance (under FreeBSD), or tell me where to find such information,
that would be great)


Thanks,

Bill