Reduce the partition size in the system. Always keep FFS partitions to under 2Gb.
I was about to comment this as well...
Ive had ghost drives showing up in my SCSI chain when i had partitions larger than 4 gig... The partition failed and erased all my data shortly after.
After som good advices from people here in a.org my boot partition is always the first one on a drive and never exceeds 1 gig. i think the boot partitions are 500meg or less on all my computers now.
I have never had any problems with my scsi chain(s) after that.