> SATA and SCSI/SAS should give comparable single work-load sequential > numbers, but most SCSI/SAS have better seek times so random IO will > be better on those. Also SCSI/SAS support tagged command queuing, > which allows multiple overlapping IOs so you will tend to see better > mixed workload performance compared to SATA (multi-user environment). > > Having said that some of the new SATA models that support NCQ, the > SATA version of TCQ, and that use some of the same SCSI/SAS onboard > processing (Western Digital Raptors) can approach or equal SCSI/SAS > mixed load performance, but their price also approaches or equals > SCSI/SAS and their spindle speeds still do not top 10K so random > will not be as good. Nope. SATA drives with NCQ support are in the same price range as non NCQ drives, if not the same price, which is by far less costly than SCSI/SAS drives. Also, due to the incredible packing to get 200GB-750GB of space onto the platter, the lower RPM is made up for especially at the higher densities. A 73GB 15K RPM SCSI/SAS drive is in the same price range as a 750GB 7.5K RPM NCQ capable SATA drive. Ten times the density at half the speed. I reckon it would give the SCSI drive a run for its money in regard to random access times. The SCSI drive: Spindle Speed 15000 rpm Average latency 2.0 msec Random read seek time 3.50 msec Random write seek time 4.0 msec The SATA drive: Spindle Speed 7200 rpm Native Command Queuing Y Average latency 4.16 msec Random read seek time <8.5 msec Random write seek time <10.0 msec Maximum interface transfer rate 300 Mbytes/sec Without NCQ enabled, it will take twice as long as the scsi drive. With NCQ enabled, the game changes. Compare to a 10K scsi drive: Spindle Speed 10,000 rpm Sustained data transfer rate 80 Mbytes/sec. Average latency 3.0 msec Random read seek time 4.9 msec Random write seek time 5.4 msec Maximum interface transfer rate 320 Mbytes/sec NCQ SATA is almost a no-brainer.