Low-cost Advanced Technology Attachment (ATA) disc
arrays are already gaining ground in near-line storage and
disc-to-disc backup applications, but a faster class of drive
arrays that uses the Serial ATA interface standard is likely to
challenge SCSI for high-performance applications as
well.
The Serial ATA standard, approved in November by the Institute
of Electrical and Electronics Engineers (IEEE), has several
advantages over the parallel, shared-bus master/slave architecture
of ATA.
Serial ATA works at lower voltages, and because it uses just
four data lines compared with ATA's 32, it is 50% faster.
It also supports hot-swappable drives and advanced features such
as native command queuing, which lets a disc drive make multiple
requests for data from the processor and rearrange the order of the
data to maximise throughput - a feature traditionally available
only on SCSI and fibre channel drives.
Finally, Serial ATA can support up to 128 devices per channel
and extends the maximum supported cable length from 18in to 1m.
Serial ATA's biggest potential benefit lies in its
price/performance. Analyst company IDC estimated that about 87% of
all drives today use ATA.
Economies of scale have made ATA disc arrays, at 1 to 2 cents
per megabyte, much cheaper than SCSI, at 3 to 5 cents per
megabyte.
Serial ATA disc arrays should benefit from those same economies
and could displace SCSI in small servers and even large storage
arrays using the emerging iSCSI storage networking protocol.
"Five to 10 years from now, Serial ATA with iSCSI will be the
dominant storage model," predicted IDC analyst Robert Grey.
Serial ATA's first incarnation, available in drives and
controllers, will not benefit end users because ATA disc speeds, at
a maximum sustained throughput rate of about 75MB/sec cannot use
the bandwidth increase that Serial ATA offers.
Initial pricing will be about 10% higher than for ATA drives,
says Jason Ziller, chairman of the IEEE's Serial ATA Working
Group.