Dell SAS5 Performance Issue

[Richard Tector]

I'm suffering from very slow write performance on a Dell PowerEdge 860 
with the SAS5/IR controller (mpt driver) running either 6.2-RELEASE or 
6.2-STABLE with sources from yesterday. The controller hosts 2 Western 
Digital 320GB SATA disks in a RAID1 configuration.
Reads approach 65MB/s however writes appear extremely slow, in the 
region of 6-7MB/s with a dd and a blocksize of 1MB all the way down to 
about 300KB/s while extracting a ports snapshot.

It was suggested to me that perhaps write caching has been disabled on 
the controller however no options exist within the BIOS configuration to 
view/adjust *any* caching options.

Has anyone else experienced this issue? If so how did they resolve it?
Also, is there any way to toggle the caching settings from FreeBSD?

Regards,

Richard Tector