Re: ZFS with Linux: An Open Plea

[Valerie Henson <val_henson@linux.intel.com>]

On Wed, Apr 18, 2007 at 01:25:19PM -0400, Lennart Sorensen wrote:
> 
> Does it matter that google's recent report on disk failures indicated
> that SMART never predicted anything useful as far as they could tell?
> Certainly none of my drive failures ever had SMART make any kind of
> indication that anything was wrong.

I saw that talk, and that's not what I got out of it.  They found that
SMART error reports _did_ correlate with drive failure.  See page 8
of:

http://www.usenix.org/events/fast07/tech/full_papers/pinheiro/pinheiro.pdf

(If you're not a USENIX member, you may be able to find a free
download copy elsewhere.)

However, they found that the correlation was not strong enough to make
it economically feasible to replace disks reporting SMART failures,
since something like 70% of disks were still working a year after the
first failure report.  Also, they found that some disks failed without
any SMART error reports.

Now, Google keeps multiple copies (3 in GoogleFS, last I heard) of
data, so for them, "economically feasible" means something different
than for my personal laptop hard drive.  I have twice had my laptop
hard drive start spitting SMART errors and then die within a week.  It
is economically quite sensible for me to replace my laptop drive once
it has an error, since I don't carry around 3 laptops everywhere I go.

-VAL
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