Re: [BUG] e2fsprogs & ext2/3 behave poorly with corrupt group descriptors

On Aug 23, 2006  21:05 -0400, Benjamin LaHaise wrote:
> On Wed, Aug 23, 2006 at 04:46:36PM -0600, Andreas Dilger wrote:
> > What about using one of the backup group descriptors?  I'm not sure about
> > e2image, but e2fsck should try that automatically (older versions were
> > worse at that, and if there is still a problem for e2fsck to find backups
> > this should be fixed).  The kernel can be told to use a backup with
> > "-o sb=32768" (or 32768 * {3,5,7}^n) when mounting (assuming 4kB blocksize).
> 
> Doesn't particularly seem to help in mounting the filesystem:
> 
> [root@woody spare]# mount -t ext3 -o loop,ro,sb=8277 laptop.img mnt/
> EXT3-fs error (device loop0): ext3_check_descriptors: Block bitmap for group 0 !
> EXT3-fs: group descriptors corrupted!                                           
8277 is almost certainly not a superblock, unless you have something
VERY strange going on.  I'd suspect this is a superblock copy in the
journal.  For filesystems > 512MB the first backup is at 32768, the
second at $((32768 * 3)), next at $((32768 * 5)).  For 1kB filesystems
(default for < 512MB) they are at (8192 * {3,5,7}^n + 1), so 8193,
24577, ...

> At the very least e2image needs to be taught to do the right thing
> with this sort of corruption.

By all means...

Does e2fsck not work either?

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.


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