Re: Unable to mount, corrupt leaf

[Hugo Mills <hugo@carfax.org.uk>]

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On Tue, May 28, 2019 at 03:39:36PM -0300, Cesar Strauss wrote:
> Hello,
> 
> After a BTRFS partition becoming read-only under use, it cannot be
> mounted anymore.
> 
> The output is:
> 
> # mount /dev/sdb5 /mnt/disk1
> mount: /mnt/disk1: wrong fs type, bad option, bad superblock on
> /dev/sdb5, missing codepage or helper program, or other error.
> 
> Kernel output:
> [ 2042.106654] BTRFS info (device sdb5): disk space caching is enabled
> [ 2042.799537] BTRFS critical (device sdb5): corrupt leaf: root=2
> block=199940210688 slot=31, unexpected item end, have 268450090
> expect 14634

   You have bad RAM.

The item end it's got on the disk:
>>> hex(268450090)
'0x1000392a'

The item end it should have (based on the other items and their
lengths and positions):
>>> hex(14634)
'0x392a'

   The good checksum on the block (it hasn't complained about the
csum, so it's good) indicates that the corruption happened in memory
at some point. The bit-flip in the data would strongly suggest that
it's caused by a stuck memory cell -- i.e. bad hardware.

   Run memtest86 for a minimum of 8 hours (preferably 24) and see what
shows up. Then fix the hardware.

   Hugo.

> [ 2042.807879] BTRFS critical (device sdb5): corrupt leaf: root=2
> block=199940210688 slot=31, unexpected item end, have 268450090
> expect 14634
> [ 2042.807947] BTRFS error (device sdb5): failed to read block groups: -5
> [ 2042.832362] BTRFS error (device sdb5): open_ctree failed
> 
> # btrfs check /dev/sdb5
> Opening filesystem to check...
> incorrect offsets 14634 268450090
> incorrect offsets 14634 268450090
> incorrect offsets 14634 268450090
> incorrect offsets 14634 268450090
> ERROR: cannot open file system
> 
> Giving -s and -b options to "btrfs check" made no difference.
> 
> The usebackuproot mount option made no difference.
> 
> "btrfs restore" was successful in recovering most of the files,
> except for a couple instances of "Error copying data".
> 
> System information:
> 
> OS: Arch Linux
> 
> $ uname -a
> Linux rescue 5.1.4-arch1-1-ARCH #1 SMP PREEMPT Wed May 22 08:06:56
> UTC 2019 x86_64 GNU/Linux
> 
> $ btrfs --version
> btrfs-progs v5.1
> 
> I have since updated the kernel, with no difference:
> 
> $ uname -a
> Linux rescue 5.1.5-arch1-2-ARCH #1 SMP PREEMPT Mon May 27 03:37:39
> UTC 2019 x86_64 GNU/Linux
> 
> Before making any recovery attempts, or even restoring from backup,
> I would like to ask for the best option to proceed.
> 
> Thanks,
> 
> Cesar

-- 
Hugo Mills             | You've read the project plan. Forget that. We're
hugo@... carfax.org.uk | going to Do Stuff and Have Fun doing it.
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                           Jeremy Frey

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