Re: ZFS with Linux: An Open Plea

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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