From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: fsck.ext4: Group descriptors look bad... trying backup blocks...
Date: Fri, 17 Apr 2009 12:00:29 -0500
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To: Jeremy Sanders <jss@ast.cam.ac.uk>
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Jeremy Sanders wrote:
> Hi - I'm trying out ext4 on a large 8.2 TB software raid device (md). On 
> rebooting (cleanly unmounting), I tried an fsck on the device. I get the 
> following:
> 
> [root@xback2 ~]# fsck /dev/md0
> fsck 1.41.4 (27-Jan-2009)
> e2fsck 1.41.4 (27-Jan-2009)
> fsck.ext4: Group descriptors look bad... trying backup blocks...
> Group descriptor 0 checksum is invalid.  Fix<y>?
> 
> It then finds lots of bad group descriptors.
> 
> This is Fedora 10, 2.6.27.21-170.2.56.fc10.x86_64 and 
> e2fsprogs-1.41.4-4.fc10.x86_64.
> 

Jeremy, if you're willing, could you upgrade to the 2.6.29 kernel that's
in F10 updates-testing?  That way the ext4 code is a bit more of a
recent, common codebase.  Also, if this is a test fs, re-mkfs'ing from
scratch might not be a bad way to go.

Depending on how hard it is to reproduce, it may also be interesting to
try a filesystem just shy of 8TB (2^31) blocks in case there is some
32-bit wrap-around there, since you're at 8.2T....

-Eric