linux-ext4 - Re: Issue with bad file system

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Date:	Mon, 19 Nov 2012 19:53:13 +0000
From:	Drew Reusser <dreusser@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	George Spelvin <linux@...izon.com>, linux-ext4@...r.kernel.org
Subject: Re: Issue with bad file system

On Mon, Nov 19, 2012 at 6:41 PM, Theodore Ts'o <tytso@....edu> wrote:
> One of the things you could to verify that in fact the RAID array is
> sane is to run the following command:
>
> debugfs -s 32768 -b 4096 /dev/md0
>
> Then you can examine the file system via the debugfs commands "cd",
> "ls", "cat", "dump" (or even "rdump", although that's more interesting
> recovery operations).  I would suggest looking at a number of
> directories and make sure they look as you expect them, and that you
> try dumping out a few files and making sure that they are
> uncorrecpted.
>
> If the majority of the files you look at look sane, then it should be
> safe to let e2fsck recover the file system from the backup superblock.
>
> In the future, we'll be able to use the metadata checksum feature to
> automate this process (as well as being able to more gracefully and
> automatically handle inode table blocks written to the wrong location
> on disk, overwriting other inode table blocks) --- but a bit more
> testing is needed before I'd recommend it for regular users.  (In
> particular, I want to make sure that random journal corruptions are
> handled correctly when the metadata checksum feature is enabled ---
> before we start having more enthusiastic users try out bleeding edge
> features on production file systems....)
>
> Regards,
>
>                                                 - Ted

Sorry Ted, but that is not working.

mint mnt # debugfs -s 32768 -b 4096 /dev/md0
debugfs 1.42.5 (29-Jul-2012)
/dev/md0: Bad magic number in super-block while opening filesystem
debugfs:
debugfs:  ls
ls: Filesystem not open
debugfs:
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