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.
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