Performance problem with adaptec 2120S

[amon at sockar.homeip.net]

hi,

I have a problem with my new adaptec 2120S, I cannot get more than 
3 MB/s when writing to it.

My card has firmware 4.0-0[6008] and is connected to an sca backplane
with 3 ultra 160 disks on it, all in a single RAID 5 volume. The card
is plugged in a 32 bits/33 Mhz pci slot and the installed freebsd version
is 4.9-R.

When I do a file transfer from another box, I see in systat that aac0
is 100% busy at 3MB/s during the copy. Since this card is U320, I sincerely
hope it can do better but I couldn't find the source of the problem.
I tried setting all devices at 160MB/s non packetized in the controller
config with no luck. Same thing with other disks.

Is this a known issue ?

I can provide full dmesg if necessary.

-- 
Herve Boulouis