[nSLUG] hard disks can't be trusted (as if you didn't already know that)

Mark Lane lmlane at gmail.com
Sun Mar 4 21:30:34 AST 2007

On 3/4/07, Stephen Gregory <nslug at kernelpanic.ca> wrote:
> On 4-Mar-07, at 16:27 , George N. White III wrote:
> > Google's study is for consumer grade disks, but their overall
> > failure rates aren't out of line with other studies.
> The Google study is interest, but there is a slight problem: they
> don't distinguish between failure types. The study study states that
> failures such as controller failure were also counted as drive
> failures. This does not make the study worthless, but the conclusions
> should be more along the lines of: "more study needed." Probably the
> most interesting aspect of the study is that SMART is a poor
> indicator of drive health.
> A Carnegie Mellon U study published at the same conference is also
> interesting. They also found no bath-tub effect. They found that
> failure rates were significantly higher then manufacturers claims.
> The study found no correlation between failure and SCSI, FCAL, or
> SATA. However it is not clear if the SATA drives are desktop drives
> or server grade "near-line" drives.
> http://www.usenix.org/events/fast07/tech/schroeder.html
> I definitely want to see more studies on consumer grade versus server
> grade drives. In the lab we have two Sun raid arrays and we had an
> Apple raid. Sun uses stupid expensive SCSI drives. Apple uses cheap
> desktop (not even semi-server) IDE drives in FCAL to IDE sleds. The
> drives in the Apple raid failed so often that it was decommissioned
> in less then a year. There are twice as many SUN drives in operation
> since 2001 and I think only one drive has ever failed. Obviously
> there are not enough drives to draw any conclusions from, but it has
> made us reconsider using cheaper desktop hard drives. (It doesn't
> hurt that SUN, IBM, Dell, and HP will courier a drive to me in 1 day
> and Apple won't.)

The make of the IDE will make a difference. For instance, Maxtor makes
crap. I use to sell SATA based RAID arrays for a living. The
manufacturer makes all the difference and the newer raid configured
SATA drives last better in arrays. You can get bad runs from any
manufacturer and that includes SCSI drives.

The question is how much space do you need. If you need a ton of
space, SATA offers a much more cost effective solution. You can build
in more redundancy and still save a ton over a similar SCSI solution.
Also when you get in to arrays over about 4 drives, the extra speed of
the SCSI drives becomes neglectable because the limiting factor
becomes the bus speed.

Western Digital SATA Raid drives come with the same Mean time to
failure as a SCSI drive and same 5 year Warranty.

The biggest reason SCSI drives are still the Enterprise is because
they are the established and trusted technology --- not because they
are necessarily any better.

Mark Lane, CET <lmlane at gmail.com>


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