Re: btrfs check: backref lost, mismatch with its hash -- can't repair

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

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On 2018年01月29日 22:49, ^m'e wrote:
> On Mon, Jan 29, 2018 at 2:04 PM, Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>>
>>
>> On 2018年01月29日 21:58, ^m'e wrote:
>>> Thanks for the advice, Qu!
>>>
>>> I used the system for a while, did some package upgrades -- writing in
>>> the suspect corrupted area. Then tried a btrfs-send to my backup vol,
>>> and it failed miserably with a nice kernel oops.
>>>
>>> So I went for a lowmem repair:
>>> ----------------------------------------------------------------------------------------
>>> # ./btrfsck.static check --repair --mode=lowmem /dev/sdb3 2>&1 | tee
>>> /mnt/custom/rescue/btrfs-recovery/btrfs-repair.BTR-POOL.1.log
>>> WARNING: low-memory mode repair support is only partial
>>> Fixed 0 roots.
>>> checking extents
>>> checking free space cache
>>> checking fs roots
>>> ERROR: failed to add inode 28891726 as orphan item root 257
>>> ERROR: root 257 INODE[28891726] is orphan item
>>
>> At least I need dig the kernel code further to determine if the orphan
>> inode handling in btrfs-progs is correct or not.
>>
>> So there won't be more dirty fix soon.
>>
>> Hopefully you could get some good backup and restore the system.
>>
>> At least the problem is limited to a very small range, and it's
>> something we could handle easily.
>>
>> Thanks for all your report,
>> Qu
>>
>>
> 
> Right.
> 
> Meanwhile, could you please suggest the best course of action? btrfs
> rescue or restore?
> I have snapshots of my two subvols (rootfs, home -- now fs-checking
> them  just in case...)

Don't run --repair any more.
It seems to make the case worse.

While the RW mount with orphan cleanup abort seems to screwed up the
filesystem.

In this case, it's pretty hard to recover, but still has small chance.

Use btrfs inspec dump-super to get backup roots:

# btrfs inspect dump-super -fFa <device> |grep backup_tree_root: | sort
| uniq

And try all the 4 numbers in the following commands:

# btrfs check --tree-root <number> <device>

To see if is there any good one without transid error.

Thanks,
Qu

> 
> Cheers,
> 
>   Marco
> 


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