[Cialug] SATA v. SCSI

[Don Cady]

Nate, from previously (albeit when they first came out) looking at the specs
of SATA drives it seems to me there are two "classes" of the drives. A
'consumer' class that are cousins of IDE/ATA drives, and an
'workstation/small-server' class that
are cousins of low-end SCSI drives.
The specs were fairly close between some models. On others, it's so close
that all other physical properties, such as platters, density, rpms, cache,
temp limits, seek, etc, are exactly the same.
I think you've stumbled upon the second. To me, they're drives with SCSI
pedigrees, but with SATA interfaces instead.

Don

> Wow, thanks for the great write-up, that's very re-affirming.
>
> I have a PIII 900 Mhz as my main workstation at work and the SCSI drive is
> probably what keeps it usable/tolerable.
>
> Those new Sun SAS drives look scary.  Or maybe I mean dainty - if I am
> thinking of the right ones.
>
> I've also noticed there are some "special" SATA drives designated for use 
> in
> server or RAID applications.  They come at a premium price.  I'm not sure
> how they differ from standard consumer drives, if at all.
>
> -Nate
>
>> -----Original Message-----
>> From: Randy Rote [mailto:randy.rote at gmail.com]
>> Sent: Thursday, May 11, 2006 9:53 PM
>> To: Central Iowa Linux Users Group
>> Subject: Re: [Cialug] SATA v. SCSI
>>
>> 300 MB/s is the rated speed of the SATA II bus and 320 MB/s
>> is the speed of the
>> Ultra 320 SCSI bus.   I'm sure you could get a drive to do
>> small burst transfers
>> from cache at this speed, but the sustained rate of the top
>> end drives is just shy of 100 MB/s right now.
>>
>> SCSI is still king of the hill in terms of absolute maximum
>> throughput and latency.  A lot of this advantage comes with
>> the 15K rpm speeds.  However, the performance comes at a
>> price. SATA drives give you more capacity per dollar, with
>> roughly twice the average access time.
>>
>> Storage Review has some great reading material on this subject.
>>
>>   Performance comparisons:
>> http://www.storagereview.com/comparison.html
>>
>>   Reference Guide:
>> http://www.storagereview.com/guide2000/ref/hdd/perf/perf/spec/
>> trans.html
>>
>> Western Digital has a white paper on the topic.  This is a
>> marketing tool though, so it should be taken with a grain of
>> salt, but it's a great overview.
>> http://westerndigital.com/en/library/sata/2579-001097.pdf  __(PDF)__
>>
>> Some digging through google also turned up a related
>> discussion on Slashdot.
>> http://ask.slashdot.org/article.pl?sid=06/01/24/2332240
>>
>>
>> Bottom line though, it depends on your application.  If
>> you're running a server that needs to grab data from all over
>> the disk in little chunks, scsi is probably the best fit.
>> For larger sustained transfers, the SATA compares pretty
>> favorably.  If you're on a budget and need to maximize
>> capacity, SATA is the way to go.  For most cases, the extra
>> cost of the SCSI drives probably isn't worth it.  A lot of
>> enterprise level vendors are shipping serial interface drives
>> with new systems.  Sun's new servers, both the AMD Opteron
>> and UltraSPARC T1 systems are shipping with SAS drives now.
>> Western Digital has made it seemingly impossible to purchase
>> a new SCSI drive. Maybe I'm not looking hard enough.
>>
>> As far as reliability, SATA II drives haven't really been
>> around long enough (mid 2004 I think) to get a good feel for
>> long-term reliability yet.  Most are probably still under
>> warranty.  Your best bet would be to stick with vendors
>> offering 5 year warranties on their drives. If they're
>> offering a guarantee, it's a safe bet that they're sure the
>> drive will last at least that long.
>>
>> --
>> Randy Rote
>> Simon Tire & Cellular -- Information Systems Specialist
>> Phone: 515.282.0205
>>
>> Nathan C. Smith wrote:
>> > I've seen SATA and SCSI drives (ultra SCSI) list speeds of
>> 300Mb/s.
>> > Is this the raw transfer speed of the interface or the
>> speed from disk
>> > to bus or is that the hidden marketing element in these
>> advertised speeds?
>> >
>> > It boils down to this:  assuming you have a good SATA
>> controller or a
>> > good SCSI controller, are the disk subsystems going to be
>> on par with each other?
>> > Can SATA be seriously considered as a replacement for SCSI yet?
>> >
>> > -Nate
>> >
>> > Nathan Smith  McKee, Voorhees & Sease, P.L.C.  515.288.3667
>> > _______________________________________________
>> > Cialug mailing list
>> > Cialug at cialug.org
>> > http://cialug.org/mailman/listinfo/cialug
>> >
>>
>>
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