Troubleshooting a 3Ware 9550SX under 6.3

[Adam Bayless]

I've recently noticed slow performance on a machine that runs amanda and stores 
backups for our network on a RAID-5. It was running 6.2. I upgraded to 6.3 just 
today, so it is completely up to date on the 6 branch. Here's hopefully most of the 
relevant info:

6.3-STABLE FreeBSD 6.3-STABLE #0: Mon Jun  9 12:57:40 MDT 2008 
me at machine:/usr/obj/usr/src/sys/GENERIC  amd64

da0 at twa0 bus 0 target 0 lun 0
da0: <AMCC 9550SX-12  DISK 3.04> Fixed Direct Access SCSI-3 device
da0: 100.000MB/s transfers
da0: 2145735MB (4394465280 512 byte sectors: 255H 63S/T 273542C)

hw.twa0.driver_version: 3.60.04.003

Unit  UnitType  Status         %Cmpl  Stripe  Size(GB)  Cache  AVerify  IgnECC
------------------------------------------------------------------------------
u0    RAID-5    OK             -      64K     2095.44   OFF    OFF      OFF

Port   Status           Unit   Size        Blocks        Serial
---------------------------------------------------------------
p0     OK               u0     698.63 GB   1465149168    3QD0TAVV
p1     NOT-PRESENT      -      -           -             -
p2     NOT-PRESENT      -      -           -             -
p3     NOT-PRESENT      -      -           -             -
p4     OK               u0     698.63 GB   1465149168    3QD0SYE3
p5     NOT-PRESENT      -      -           -             -
p6     NOT-PRESENT      -      -           -             -
p7     NOT-PRESENT      -      -           -             -
p8     OK               u0     698.63 GB   1465149168    3QD0SE36
p9     OK               u0     698.63 GB   1465149168    3QD0THRB
p10    NOT-PRESENT      -      -           -             -
p11    NOT-PRESENT      -      -           -             -

Filesystem  1K-blocks        Used     Avail Capacity  Mounted on
/dev/da0s1a    4058062      96518   3636900     3%    /
devfs                1          1         0   100%    /dev
/dev/da0s2d 1914817666 1647878588 113753666    94%    /backup
/dev/da0s1d    4058062       3344   3730074     0%    /tmp
/dev/da0s1f  171626538    7978766 149917650     5%    /usr
/dev/da0s1e   25385516     124322  23230354     1%    /var

I'm getting performance like this (no other processes were running at this time):

dd if=/dev/zero of=testfile
165760+0 records in
165759+0 records out
84868608 bytes transferred in 25.028232 secs (3390915 bytes/sec)

I think I ought to be able to get more than 3.2MB/sec out of this card, right? The 
machine is about a year old and I am pretty sure it wasn't anywhere near this slow at 
the beginning, though I don't have any numbers from that time to back up that 
opinion. What else can I try to get more info or resolve the issue? I've looked 
online for others complaining of slowness and most of the chatter about twa on 
freebsd seems to be about the driver having been missing from certain install discs 
back in the day. No one else seems to be having speed issues.

Thanks!!

-adam