Re: SCSI vs SATA - Mailing list pgsql-performance

At 11:19 AM 4/5/2007, Scott Marlowe wrote:
>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.

Exactly correct.


>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.

Also exactly correct.  High temperatures or unclean power issues age
HDs faster than any other factors.

This is why I dislike 1U's for the vast majority f applications.


>I would, however, allocate 3 or 4 drives as spares in the 36 drive
>array just to be sure.
10% sparing is reasonable.


>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.

Yeah, that was very much !no! fun.


>  Until the drives have been burnt in and proven reliable, just
> assume that they could all fail at any time and act accordingly.
Yep.  Folks should google "bath tub curve of statistical failure" or
similar.   Basically, always burn in your drives for at least 1/2 a
day before using them in a production or mission critical role.


Cheers,
Ron Peacetree