Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck)

[Andreas Dilger <adilger@sun.com>]

On Jan 15, 2008  22:05 -0500, Rik van Riel wrote:
> With a filesystem that is compartmentalized and checksums metadata,
> I believe that an online fsck is absolutely worth having.
> 
> Instead of the filesystem resorting to mounting the whole volume
> read-only on certain errors, part of the filesystem can be offlined
> while an fsck runs.  This could even be done automatically in many
> situations.

In ext4 we store per-group state flags in each group, and the group
descriptor is checksummed (to detect spurious flags), so it should
be relatively straight forward to store an "error" flag in a single
group and have it become read-only.

As a starting point, it would be worthwhile to check instances of
ext4_error() to see how many of them can be targetted at a specific
group.  I'd guess most of them could be (corrupt inodes, directory
and indirect blocks, incorrect bitmaps).

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