Re: [RFD] Incremental fsck

Andi Kleen wrote:
Theodore Tso <tytso@xxxxxxx> writes:
Now, there are good reasons for doing periodic checks every N mounts
and after M months. And it has to do with PC class hardware. (Ted's
aphorism: "PC class hardware is cr*p").

If these reasons are good ones (some skepticism here) then the correct
way to really handle this would be to do regular background scrubbing
during runtime; ideally with metadata checksums so that you can actually
detect all corruption.

But since fsck is so slow and disks are so big this whole thing
is a ticking time bomb now. e.g. it is not uncommon to require tens
of minutes or even hours of fsck time and some server that reboots
only every few months will eat that when it happens to reboot.
This means you get a quite long downtime.

Has there been some thought about an incremental fsck?

While an _incremental_ fsck isn't so easy for existing filesystem types,
what is pretty easy to automate is making a read-only snapshot of a
filesystem via LVM/DM and then running e2fsck against that. The kernel
and filesystem have hooks to flush the changes from cache and make the
on-disk state consistent.

You can then set the the ext[234] superblock mount count and last check
time via tune2fs if all is well, or schedule an outage if there are
inconsistencies found.

There is a copy of this script at:
http://osdir.com/ml/linux.lvm.devel/2003-04/msg00001.html

Note that it might need some tweaks to run with DM/LVM2 commands/output,
but is mostly what is needed.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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