On Thursday 25 September 2008 19:14, someone identifying as *David Lesher*
wrote in /comp.os.linux.hardware:/

> Aragorn writes:
>
>> I'm not so sure that's a market trend. It just so happens to be that
>> SCSI is no longer considered useful in the home and office desktop
>> market, but servers are most definitely still using SCSI.
>>
>> However, the SCSI that's being used and marketed today is no longer of
>> the parallel variant. Just as parallel ATA had to make way for serial
>> ATA, SCSI has by now already started making way for serial attached SCSI
>> (SAS) and iSCSI for storage area networks.
>
> I'm sorry, but you'll have go a long way to convince me the parentage of
> SAS is anything but:
>
> MarketDroid 1): Damn, everyone is buying SATA drives; the price is
> falling and we are screwed. How do we come up with a way to charge a
> premium without really doing a lot of work?
>
> MD2: I've got it! We'll rebadge SATA into something with SCSI in the
> name, so it sounds beefier... hmmm that's it.. Serial Attached SCSI.
> We save the investment in ""SCSI"" and build up the hype around it.
>
> MD1: But SATA really has some pluses.. Are we going to ignore them?
>
> MD2: We'll use Gate's ploy -- extend and embrace! We'll tweek some
> SATA specs here and there, adding some things we can talk up. But
> we'll save a bundle on connectors alone.

As with everything, technology is mainly developed to get marketed rather
than for progress, but SAS is far more than what you describe above.

The serialization of SCSI does offer some benefits with regard to large
enterprises and data centers, and it all falls within the spirit of
extending the possibilities of SCSI, e.g. there is also iSCSI now, which is
a SCSI tunnel over ethernet.

> In the past, SCSI server drives brought you two things: performance and
> reliability. [Think of those 9 GB Barracudas..].

It still does. The drives themselves - or at least, the ones I know - are
basically the same as the U320 drives, but their maximum throughput is
higher, whereas you could end up with a bottleneck on parallel SCSI chains.

> Now the issues are: Does SAS really do that much over SATA, for your
> case? And: Does paying SAS prices really give you more reliable drives,
> or just different electronics?

SAS drives *are* SCSI drives, so they do have all the goodies that SCSI
comes with - e.g. ECC, logging, tagged command queueing - whereas SATA is
actually nothing other than a serialized ATA drive in which an attempt was
made to make ATA/IDE more SCSI-like.

Enterprise-grade SATA drives are probably just or nearly as reliable as
SAS/SCSI, but they lack the features that made SCSI stand out. SATA still
is ATA, don't forget that. ;-) Also, not all SATA drives - not even in the
enterprise-grade range - are fit to be used in RAID arrays, while SAS
drives all are RAID-rated.

On the other hand, if you care more about cost-effectiveness than features,
then SATA offers (far) more storage per Dollar/Euro than SCSI. But then
again, this was already the case for PATA - aka IDE, although SATA is IDE
as well - versus parallel SCSI.

So the bottom line is that if you're thinking about marketing scams, the
scam would rather rest with SATA than with SAS, because SATA was intended
to mimic SCSI over an IDE bus, but still has to rely on the SATA-specific
NCQ (native command queueing) over the SCSI-specific TCQ (tagged command
queueing), because TCQ on SATA sucks. Also, the difference in retail price
between a SAS disk and an U320 SCSI disk is mainly negligible.

--
*Aragorn*
(registered GNU/Linux user #223157)