linux-ext4 - Re: Recovering a damaged ext4 fs

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Message-id: <20090206062901.GM3209@webber.adilger.int>
Date:	Thu, 05 Feb 2009 23:29:02 -0700
From:	Andreas Dilger <adilger@....com>
To:	"J.D. Bakker" <jdb@...tmaker.nl>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Recovering a damaged ext4 fs - revisited.

On Feb 06, 2009  04:06 +0100, J.D. Bakker wrote:
> On reboot the system refused to auto-fsck /dev/md0. A manual e2fsck -nv 
> /dev/md0 reported:
>
>   e2fsck 1.41.4 (27-Jan-2009)
>   ./e2fsck/e2fsck: Group descriptors look bad... trying backup blocks...

Not sure why it considers the initial group descriptors bad.

>   Group descriptor 0 checksum is invalid.  Fix? no
>   Group descriptor 1 checksum is invalid.  Fix? no
>   Group descriptor 2 checksum is invalid.  Fix? no
>   [...]
>   Group descriptor 29808 checksum is invalid.  Fix? no

Note that the checksums in the backup blocks are probably incorrect, so
this isn't itself a problem.

>   newraidfs contains a file system with errors, check forced.
>   Pass 1: Checking inodes, blocks, and sizes
>   Pass 2: Checking directory structure
>   Pass 3: Checking directory connectivity
>   Pass 4: Checking reference counts
>   Pass 5: Checking group summary information
>   Block bitmap differences:  [...]
>   Fix? no
>   Free blocks count wrong for group #0 (23513, counted=464).
>   Fix? no
>   Free blocks count wrong for group #1 (31743, counted=509).
>   Fix? no
>   [...]
>   Free inodes count wrong for group #7748 (8192, counted=940).
>   Fix? no
>   Directories count wrong for group #7748 (0, counted=1).
>   Fix? no
>   Free inodes count wrong for group #7749 (8192, counted=8059).
>   Fix? no
>   Free inodes count wrong (244195317, counted=237646747).
>   Fix? no

These also look like trivial errors, due to using the backup group
descriptors (which are not kept up-to-date.  It appears from this
e2fsck output that there isn't really anything wrong with the fs.

>   Error writing block 1 (Attempt to write block from filesystem resulted 
> in short write).  Ignore error? no
>   Error writing block 2 (Attempt to write block from filesystem resulted 
> in short write).  Ignore error? no
>   Error writing block 3 (Attempt to write block from filesystem resulted 
> in short write).  Ignore error? no

This is a serious problem.

> As I said, is there anything I can do to recover my data, or to make  
> sure this doesn't happen again?

I would say to run "e2fsck -fp /dev/XXX" and your data _should_ be
there.

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

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