linux-kernel - Re: ZFS with Linux: An Open Plea

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Message-ID: <20070427052102.GD20286@nifty>
Date:	Thu, 26 Apr 2007 22:21:02 -0700
From:	Valerie Henson <val_henson@...ux.intel.com>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:	Tomasz K?oczko <kloczek@...y.mif.pg.gda.pl>,
	Diego Calleja <diegocg@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Mike Snitzer <snitzer@...il.com>, Neil Brown <neilb@...e.de>,
	"David R. Litwin" <presently42@...il.com>,
	linux-kernel@...r.kernel.org
Subject: 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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