Patrick Westenberg put forth on 12/15/2010 7:28 AM:
Won't be 15k U320 SCSI disks also faster than average SATA disks for the indexes?
Yes. A faster spindle speed allows for greater random IOPS. Index file reads/writes are random IOPS, and become more random with greater concurrency, i.e. more users.
Although, I should point out that parallel SCSI (U320) is pretty much a dead technology at this point. AFAIK, no vendor has shipped a new parallel SCSI disk line (only warranty replacements) for a number of years now. It has been superseded by Serial Attached SCSI (SAS).
I should also point out that the interface itself, whether parallel SCSI, SAS, or SATA, makes little difference for random IOPS performance, as long as the interface is running below the saturation point. The spindle speed and the drive firmware, specifically the queuing implementation, are what make for a good transactional performance disk drive. Typically, 15k drives have the best transactional performance, then 10k, then 7.2k, etc.
-- Stan