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Re: forced fsck (again?)



On Jan 22, 2008 8:11 AM, Eric Sandeen <sandeen redhat com> wrote:
> Eric Sandeen wrote:
> > giancarlo corti wrote:
> >> hello everyone.
> >>
> >> i guess this has been asked before, but haven't found it in the faq.
> >>
> >> i have the following issue...
> >>
> >> it is not uncommon nowadays to have desktops with filesystems
> >> in the order of 500gb/1tb.
> >>
> >> now, my kubuntu (but other distros do the same) forces a fsck
> >> on ext3 every so often, no matter what.
> >
> > Did you just update to e2fsprogs-1.40.3?
> >
> > If so, should be fixed in 1.40.4 for the most part.
> >
> > See Debian bug 454926,
> > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=454926
>
> Oh - or, if it's not running each time, and it's just a general question
> about periodic fscks, then yeah, what Larry said, I guess.
>
> Although not all filesystems do this.

This will be ironic coming from me, but I think the ext3 defaults for
forcing a file system check are a little too conservative for many
modern use cases.  The two cases I have in mind in particular are:

* Servers with long uptimes that need very low data unavailability
times.  Imagine you have a machine room full of servers that have all
been up and running happily for more than 180 days - the preferred
case.  Now imagine that the room overheats and the emergency power cut
is tripped.  Standard heat reduction is swiftly applied (i.e., open
the door and turn on a fan and hope security doesn't notice) and the
power turned back on.  Now your entire machine room will be fscking
for the next 3 hours and whatever service they provide will be
completely unavailable.  Of course, any admin worth their salt will
turn off force fsck so it only runs during controlled downtime...
won't they?

* Laptops.  If suspend and resume doesn't work on your laptop, you'll
be rebooting (and remounting) a lot, perhaps several times a day.  The
preferred solution is to get Matthew Garrett to fix your laptop, but
if you can't, fscking every 10-30 days seems a little excessive.
Desktop users who shutdown daily to save power will have similar
problems.  Distros often have the "don't fsck on battery" option and
some don't use the ext3 defaults for mkfs, but that's only a partial
solution.  In this case, it's definitely a little much to ask a random
laptop user to tune their file system.

I'm not sure what the best solution is - print warnings for several
days/mounts before the force fsck? print warnings but don't force
fsck? increase the default days/mounts before force fsck? base force
fsck intervals on write activity? - but in practice I find myself
telling people about "tune2fs -c 0 -i 0" a lot.  I use it on all my
file systems and run fsck by hand every few months (or more often when
I'm working on fsck :) ).

Disks do rot, and file systems do get corrupted, and fsck should be
run periodically, but the current system of frequent unpredictable
forced fsck at boot is probably not the best cost/benefit tradeoff for
many use cases.

-VAL


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