[Cialug] SATA v. SCSI

[Randy Rote]

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
>