Subject: Re: SCSI vs SATA
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: James Mansion <james@mansionfamily.plus.com>,
	Bruce Momjian <bruce@momjian.us>,
	"Joshua D. Drake" <jd@commandprompt.com>, mark@mark.mielke.cc,
	Andreas Kostyrka <andreas@kostyrka.org>, jason@ohloh.net,
	Geoff Tolley <geoff@polimetrix.com>, pgsql-performance@postgresql.org
In-Reply-To: <19221.1175751146@sss.pgh.pa.us>
References: <HCEPKPMCAJLDGJIBCLGHMEMGHGAA.james@mansionfamily.plus.com>
	<19221.1175751146@sss.pgh.pa.us>
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Date: Thu, 05 Apr 2007 10:19:30 -0500

On Thu, 2007-04-05 at 00:32, Tom Lane wrote:
> "James Mansion" <james@mansionfamily.plus.com> writes:
> >> Right --- the point is not the interface, but whether the drive is built
> >> for reliability or to hit a low price point.
> 
> > Personally I take the marketing mublings about the enterprise drives
> > with a pinch of salt.  The low-price drives HAVE TO be reliable too,
> > because a non-negligible failure rate will result in returns processing
> > costs that destroy a very thin margin.
> 
> Reliability is relative.  Server-grade drives are built to be beat upon
> 24x7x365 for the length of their warranty period.  Consumer-grade drives
> are built to be beat upon a few hours a day, a few days a week, for the
> length of their warranty period.  Even if the warranties mention the
> same number of years, there is a huge difference here.

Just a couple of points...

Server drives are generally more tolerant of higher temperatures.  I.e.
the failure rate for consumer and server class HDs may be about the same
at 40 degrees C, but by the time the internal case temps get up to 60-70
degrees C, the consumer grade drives will likely be failing at a much
higher rate, whether they're working hard or not.

Which brings up my next point:

I'd rather have 36 consumer grade drives in a case that moves a LOT of
air and keeps the drive bays cool than 12 server class drives in a case
that has mediocre / poor air flow in it.  I would, however, allocate 3
or 4 drives as spares in the 36 drive array just to be sure.

Last point:

As has been mentioned in this thread already, not all server drives are
created equal.  Anyone who lived through the HP Surestore 2000 debacle
or one like it can attest to that.  Until the drives have been burnt in
and proven reliable, just assume that they could all fail at any time
and act accordingly.