9. What are the most common
sources of problems with RAID?
In SCSI RAID the most common source of a wide variety of
symptoms, including data loss, is incorrect cabling and
termination. Use good quality cables which are no longer
than absolutely necessary. Provide good active termination
at the end of the SCSI bus. Use a separate terminating plug
rather than using the termination on the hard drive, to
avoid loss of termination if that drive fails or is removed.
Resource conflicts are another common source of problems.
Incorrect interrupts or no interrupt assigned, onboard controller
chips which have not been disabled when not in use, non-compliant
motherboards, and so on, can all result in system lockups,
installation aborts, and generally erratic behavior. Drive
mismatches can cause problems with the array and its performance.
Ideally, all the drives in the array should be identical,
including the firmware version on the drive itself, since
different versions of the drive firmware code can result
in differences in access speed, queuing algorithms, and
head movement optimization. Most disk manufacturers will
provide firmware updates if multiple versions have been
released over the life of a particular model.