Only momentarily working system / SFS error

Hi,

I have known for a while that my Amiga, which uses an SCSI controller (phase5) has a disk access problem. It seems to work fine for 20..35 minutes, but then inevitably stops. Sometimes it's hanging, other times it's the expansion presenting an error message in a window of its own (this, I think, is an early warning even). Today in the shell environment I tried to "dir" the RAM Disk, and Smartfilesystem reported
"There was an error while accessing this volume:

Selection timeout.
The device doesn't respond.

errorcode = 44
io_Command = 2
io_Offset = 2695168
io_Length = 8192
io_Actual = 0
"

Would all that imply any particular part of the whole or is it just ambiguous?

I haven't bothered using the CD drive lately, which is also on SCSI.