Re: Question: How can I recover this partition? (unable to find logical $hugenum len 4096)

From: Hugo Mills <hugo@carfax.org.uk>
To: Chris Murphy <lists@colorremedies.com>
Cc: Nick Lee <email@nickle.es>, linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: Question: How can I recover this partition? (unable to find logical $hugenum len 4096)
Date: Mon, 26 Aug 2013 20:31:10 +0100	[thread overview]
Message-ID: <20130826193110.GO3115@carfax.org.uk> (raw)
In-Reply-To: <E76A410A-0CEF-47D7-A501-E2DDF0230735@colorremedies.com>

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On Mon, Aug 26, 2013 at 01:10:54PM -0600, Chris Murphy wrote:
> 
> On Aug 26, 2013, at 11:41 AM, Nick Lee <email@nickle.es> wrote:
> 
> > There was a discussion on IRC a few days ago that the problem with the tree root's bloco was likely the result of either an issue with the disk itself, or the chunk tree/logical mappings. I ran the chunk recover, looked over the errors it found, and hit write. (If it failed, I was going to run something photorec, loss of organization as a side effect.)
> > 
> > I can write something more clear after my flight lands tomorrow if you want.

> I'm just curious about when to use various techniques: -o recovery,
> btrfsck, chunk-recover, zero log.

   Let's assume that you don't have a physical device failure (which
is a different set of tools -- mount -odegraded, btrfs dev del
missing).

   First thing to do is to take a btrfs-image -c9 -t4 of the
filesystem, and keep a copy of the output to show josef. :)

   Then start with -orecovery and -oro,recovery for pretty much
anything.

   If those fail, then look in dmesg for errors relating to the log
tree -- if that's corrupt and can't be read (or causes a crash), use
btrfs-zero-log.

   If there's problems with the chunk tree -- the only one I've seen
recently was reporting something like "can't map address" -- then
chunk-recover may be of use.

   After that, btrfsck is probably the next thing to try. If options
-s1, -s2, -s3 have any success, then btrfs-select-super will help by
replacing the superblock with one that works. If that's not going to
be useful, fall back to btrfsck --repair.

   Finally, btrfsck --repair --init-extent-tree may be necessary if
there's a damaged extent tree. Finally, if you've got corruption in
the checksums, there's --init-csum-tree.

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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      --- Try everything once,  except incest and folk-dancing. ---      

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