Re: Cannot mount or recover btrfs

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/12/29 下午11:05, Raviu wrote:
> Hi,
> My system suddenly crashed, after reboot I cannot mount /home any more.
> 
> `uname -a`
> Linux moonIk80 4.12.14-lp151.28.36-default #1 SMP Fri Dec 6 13:50:27 UTC 2019 (8f4a495) x86_64 x86_64 x86_64 GNU/Linux
> 
> btrfs-progs v5.4
> 
> `btrfs fi show`
> Label: none  uuid: 378faa6e-8af0-415e-93f7-68b31fb08a29
>         Total devices 1 FS bytes used 194.99GiB
>         devid    1 size 232.79GiB used 231.79GiB path /dev/mapper/cr_sda4
> 
> 
> The device cannot be mounted.
> [  188.649876] BTRFS info (device dm-1): disk space caching is enabled
> [  188.649878] BTRFS info (device dm-1): has skinny extents
> [  188.656364] BTRFS critical (device dm-1): corrupt leaf: root=2 block=294640566272 slot=104, unexpected item end, have 42739 expect 9971

As Hugo has already pointed out, this looks very like a bit flip.
Thus a memtest is highly recommended.

Also, your kernel is a little old. I'm not sure if the distro (I guess
it's openSUSE or SLE?) had all the backports, but starts from v5.2, we
had newer write-time tree-checker to even prevent such bitflip written
back to disk, thus we could catch them earlier.



This is extent tree, in theory you can always salvage the data using
`btrfs-restore`.

But that's the last resort method.

> [  188.656374] BTRFS error (device dm-1): failed to read block groups: -5
> [  188.700088] BTRFS error (device dm-1): open_ctree failed
> 
> 
> 
> `btrfs check /dev/mapper/cr_sda4`
> Opening filesystem to check...
> incorrect offsets 9971 42739
> incorrect offsets 9971 42739
> incorrect offsets 9971 42739
> ERROR: failed to read block groups: Operation not permitted
> ERROR: cannot open file system
> 
> 
If you can re-compile btrfs-progs, you can try this branch:
https://github.com/adam900710/btrfs-progs/tree/dirty_fix_for_raviu

Then use the compiled btrfs-corrupt-block (I know it's a terrible name)
to fix the fs:
# ./btrfs-corrupt-block -X /dev/dm-1

It should output what it fixed if it found anything.

Thanks,
Qu


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