[ale] Fwd: periodic fsck was Re: [patch] ext2/3: document conditions when reliable operation is possible

[Greg Freemyer]

All,

I just read the below piece of advice which was new to me.

Ted Tso, the main ext4 developer is advising users to keep
ext2/ext3/ext4 partitions on LVM volumes.  That way a snapshot can be
taken weekly and the filesystem snapshot checked.

If there are no issues, there is nothing to do.

If there are issues, then start a maintenance effort to correct the
issues on the main filesystem.

He does not detail how to do that, but I assume booting into single
user mode and doing a fsck or something similar.

Hope some of you find that informative / useful.
Greg

---------- Forwarded message ----------
From: Theodore Tso <tytso at mit.edu>
Date: Mon, Nov 9, 2009 at 9:05 AM
Subject: Re: periodic fsck was Re: [patch] ext2/3: document conditions
when reliable operation is possible
To: Pavel Machek <pavel at ucw.cz>
Cc: david at lang.hm, Rik van Riel <riel at redhat.com>, Ric Wheeler
<rwheeler at redhat.com>, Florian Weimer <fweimer at bfk.de>, Goswin von
Brederlow <goswin-v-b at web.de>, Rob Landley <rob at landley.net>, kernel
list <linux-kernel at vger.kernel.org>, Andrew Morton <akpm at osdl.org>,
mtk.manpages at gmail.com, rdunlap at xenotime.net,
linux-doc at vger.kernel.org, linux-ext4 at vger.kernel.org, corbet at lwn.net,
jack at suse.cz


On Mon, Nov 09, 2009 at 09:53:18AM +0100, Pavel Machek wrote:
>
> Well, in SUSE11-or-so, distro stopped period fscks, silently :-(. I
> believed that it was really bad idea at that point, but because I
> could not find piece of documentation recommending them, I lost the
> argument.

It's an engineering trade-off.  If you have perfect memory that is
never has cosmic-ray hiccups, and hard drives that never write data to
the wrong place, etc. then you don't need periodic fsck's.

If you do have imperfect hardware, the question then is how imperfect
your hardware is, and how frequently it introduces errors.  If you
check too frequently, though, users get upset, especially when it
happens at the most inconvenient time (when you're trying to recover
from unscheduled downtime by rebooting); if you check too infrequently
then it doesn't help you too much since too much data gets damaged
before fsck notices.

So these days, what I strongly recommend is that people use LVM
snapshots, and schedule weekly checks during some low usage period
(i.e., 3am on Saturdays), using something like the e2croncheck shell
script.

                                               - Ted
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