[NTLUG:Discuss] IO-InfoOnly: SAS, SATA, Enterprise, Desktop, Nearline

[Robert Pearson]

Some time back this question was raised:

On 10/23/06, Richard Geoffrion <ntlug at rain4us.net> wrote:
> What is it about the doubleing-in-size nature (4.5, 9, 18, 36, 73, 147
> gig)  of SCSI drives?  Why don't you see  odd sized SCSI (or SAS) drives?

The correct answer is:

On 10/23/06, steve <sjbaker1 at airmail.net> wrote:
> When the drive platter spins more rapidly, each magnetic 'bit' has
> less time to induce a voltage in the drive head.  In order to get
> enough signal from the head for the electronics to detect, the bits
> have to be physically larger so they spend more time under the drive
> head.  Larger bits mean less of them.
>
> (Actually, it's probably more due to the duration of the voltage than
> the amount of voltage...but you get the idea).
>
> Hence there is a straight trade between speed and capacity.  You double
> the speed - you halve the capacity.
>
> I presume that some marketing person decided that SCSI buyers are
> more interested in performance than capacity - with the reverse
> being true for PATA/SATA buyers.

I introduced some 'way out there" parameters:

> Robert Pearson wrote:
> > All SCSI, both parallel and serial (SAS), spin 2x faster than SATA, have
> > much more rugged construction, are dual-ported, have longer MTBF and
> > longer warranties (5 yr vs. 1 yr for SATA).
> > All of which cost money.

Now there is an excellent post at Storage Advisors detailing more differences:
<<http://storageadvisors.adaptec.com/2006/11/02/seagates-definition-of-nearline-drives>>

The parameters of interest explained in the article are:

Mean Time Before Failure (MTBF)
Rotational Vibration (RV)
data protection (or error correction) in the datapath
Error recovery
Workload management
power management
Microcode download
Write Same command

                                          |MTBF|            |Duty Cycle|
=========================================
Desktop drives (SATA)    0.6MHours    typically 8×5, or similar
Enterprise drives (SAS) 1.6MHours           24×7
Nearline drives (SATA)  1.2MHours.               ?


For the longer term there are people working on the platter media to
increase capacity in SAS drives at acceptable prices. At some point
the platter media in SATA drives could offer more Storage than the
interface can handle. This is the Access Density problem.
Article source at:
<<http://www.pbs.org/cringely/pulpit/2006/pulpit_20061026_001143.html>>

Be sure and read the comments. I found them interesting as I am not
seeing this article or any like it posted anywhere else. Is it baloney
or brilliance?