Toomas Soome wrote:

Tim Boyer wrote:

In about six months, I'm going to be in the market for a 2TB system, and
will
have to make some of the same choices. Rita, _why_ is SCSI so much
better than SATA?

current data transfer rates (lets not argue about possible future
numbers, I have some but never done research for them):

SATA: 150Mb/s (up to 1.5Gb/s?)

No. 150 M_B_/sec. 3 Gb/sec hardware is shipping, not that it has any
real-world relevance. All allocated to a single device. No drive on the
market, SCSI or SATA, is capable of sustained transfers at anything close
to this rate, so it's adequate for any purpose.

SCSI: 320Mb/s

Shared among up to 15 devices. No clear advantage to SCSI here unless you
give each device a separate channel, which gets hugely expensive very
quickly.

SAS: 3Gb/s (roadmap up to 12Gb/s)?

Again, though, shared. And you're interchanging bits and bytes. That's
about 300 MB/sec.

FC-AL: 2Gb/s (roadmap up to 10Gb/s ?)

Again, shared. And that's roughly 200 MB/sec when you allow for overhead.

reliability:
SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF

This has nothing to do with SATA vs SCSI--look up the specs on WD Raptors
and you'll find that same 1,200,000 MTBF. If you want enterprise-class
storage get enterprise-class storage.

(http://searchstorage.techtarget.com/...294586,00.html)

and some real numbers as well regarding to reliability:

Deskstar 7K400, http://www.hitachigst.com/hdd/support/7k400/7k400.htm
Error rate (non-recoverable) 1 in 10E14
Start/stops (at 40° C) 50,000

Ultrastar 15K147 http://www.hitachigst.com/hdd/support/15k147/15k147.htm
Error rate (non-recoverable) 1 in 10E15
Start/stops (at 40° C) 50,000

And if you look at the Raptor you'll find again 1 in 10E15.

in general, SATA will not replace SCSI anytime "soon", high end SCSI
will still outperform SATA in many terms... but SATA does definitely
have it's place as well.

While this is true, it is not for any of the reasons you stated. SCSI does
have a few real advantages--there's a lot more in the way of
enterprise-class host adapters and array cabinets and the like available
for one thing. For another it allows _much_ longer cables. For a third,
for now the fastest SATA drives do not match the speed or capacity of the
fastest SCSI drives, and for 10K RPM SATA drives there's no second
source--that last is a marketing issue, not a technical one--there's no
reason that 15K RPM SATA drives can't be produced by multiple vendors, it's
just that so far they've decided not to.

Further, it's all rather far afield as the problem the OP is describing
isn't really addressed by any of this. His basic problem remains that he
got a substandard array controller.

toomas

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)