LSI SAS2008 performance with mps(4) driver

[Dustin Wenz]

I'm running a build of the mps(4) driver on FreeBSD 8.2 with an LSI SAS2008 bus adapter.  The code I'm using was current as of the last commit on 2011-02-25, and is built for amd64.

I can't seem to get any better performance than about 250MB/s writes through the controller. I'm testing with a zpool of six 250MB magnetic SATA disks, doing a couple of concurrent sequential writes with dd:

dd bs=128k if=/dev/zero of=/datadisk/zero1 &
dd bs=128k if=/dev/zero of=/datadisk/zero2 &

This is in comparison to an older LSI C1068E controller using the mpt driver with an identical 6-disk zpool. Such a configuration can easily sustain 500MB/s writes.

A devlist from camcontrol reports:

scbus0 on mps0 bus 0:
<ATA ST9250410AS SDM1>             at scbus0 target 0 lun 0 (pass0,da0)
<ATA ST9250410AS SDM1>             at scbus0 target 1 lun 0 (pass1,da1)
<ATA ST9250410AS SDM1>             at scbus0 target 2 lun 0 (pass2,da2)
<ATA ST9250410AS SDM1>             at scbus0 target 3 lun 0 (pass3,da3)
<ATA ST9250410AS SDM1>             at scbus0 target 4 lun 0 (pass4,da4)
<ATA ST9250410AS SDM1>             at scbus0 target 5 lun 0 (pass5,da5)
<ATA ST9250410AS SDM1>             at scbus0 target 6 lun 0 (pass6,da6)
<ATA ST9250410AS SDM1>             at scbus0 target 7 lun 0 (pass7,da7)
scbus-1 on xpt0 bus 0:
<>                                 at scbus-1 target -1 lun -1 (xpt0)

I realize that this driver is fairly new; if there is any information that would be helpful in finding the bottleneck, I would be happy to provide it.

Thanks!

	- .Dustin