Re: SCSI vs SATA - Mailing list pgsql-performance

On Thu, 5 Apr 2007, Ron wrote:

> 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 I agree with, however I believe that this is _so_ much of a factor
that it swamps any difference that they may be between 'enterprise' and
'consumer' drives.

>
>>  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.

for this and your first point, please go and look at the google and cmu
studies. unless the vendors did the burn-in before delivering the drives
to the sites that installed them, there was no 'infant mortality' spike on
the drives (both studies commented on this, they expected to find one)

David Lang