Re: SCSI vs SATA - Mailing list pgsql-performance

Given all the data I have personally + all that I have from NOC
personnel, Sys Admins, Network Engineers, Operations Managers, etc my
experience (I do systems architecture consulting that requires me to
interface with many of these on a regular basis) supports a variation
of hypothesis 2.  Let's call it 2a:

2a= Drive manufacturers _do_ design server drives to be more reliable
than consumer drives
This is easily provable by opening the clam shells of a Seagate
consumer HD and a Seagate enterprise HD of the same generation and
comparing them.
In addition to non-visible quality differences in the actual media
(which result in warranty differences), there are notable differences
in the design and materials of the clam shells.
HOWEVER, there are at least 2 complicating factors in actually being
able to obtain the increased benefits from the better design:

  *HDs are often used in environments and use cases so far outside
their manufacturer's suggested norms that the beating they take
overwhelms the initial quality difference.  For instance, dirty power
events or 100+F room temperatures will age HDs so fast that even if
the enterprise HDs survive better, it's only going to be a bit better
in the worst cases.

*The pace of innovation in this business is so brisk that HDs from 4
years ago, of all types, are of considerably less quality than those made now.
Someone mentioned FDB and the difference they made.  Very much
so.  If you compare HDs from 4 years ago to ones made 8 years ago you
get a similar quality difference.  Ditto 8 vs 12 years ago.  Etc.

The reality is that all modern HDs are so good that it's actually
quite rare for someone to suffer a data loss event.  The consequences
of such are so severe that the event stands out more than just the
statistics would imply.  For those using small numbers of HDs, HDs just work.

OTOH, for those of us doing work that involves DBMSs and relatively
large numbers of HDs per system, both the math and the RW conditions
of service require us to pay more attention to quality details.
Like many things, one can decide on one of multiple ways to "pay the piper".

a= The choice made by many, for instance in the studies mentioned, is
to minimize initial acquisition cost and operating overhead and
simply accept having to replace HDs more often.

b= For those in fields were this is not a reasonable option
(financial services, health care, etc), or for those literally using
100's of HD per system (where statistical failure rates are so likely
that TLC is required), policies and procedures like those mentioned
in this thread (paying close attention to environment and use
factors, sector remap detecting, rotating HDs into and out of roles
based on age, etc) are necessary.

Anyone who does some close variation of "b" directly above =will= see
the benefits of using better HDs.

At least in my supposedly unqualified anecdotal 25 years of
professional experience.
Ron Peacetree



At 10:35 PM 4/6/2007, Bruce Momjian wrote:

>In summary, it seems one of these is true:
>
>         1.  Drive manufacturers don't design server drives to be more
>reliable than consumer drive
>
>         2.  Drive manufacturers _do_ design server drives to be more
>reliable than consumer drive, but the design doesn't yield significantly
>better reliability.
>
>         3. Server drives are significantly more reliable than consumer
>drives.
>