Re: recovering from "parent transid verify failed"

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

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On 2019/8/15 下午9:52, Tim Walberg wrote:
> Had to wait for 'btrfs recover' to finish before I proceed farther.
> 
> Kernel is 4.19.45, tools are 4.19.1
> 
> File system is a 3-disk RAID10 with WD3003FZEX (WD Black 3TB)
> 
> Output from attempting to mount:
> 
> # mount -o ro,usebackuproot /dev/sdc1 /mnt
> mount: wrong fs type, bad option, bad superblock on /dev/sdc1,
>        missing codepage or helper program, or other error
> 
>        In some cases useful info is found in syslog - try
>        dmesg | tail or so.
> 
> Kernel messages from the mount attempt:
> 
> [Thu Aug 15 08:47:42 2019] BTRFS info (device sdc1): trying to use backup root at mount time
> [Thu Aug 15 08:47:42 2019] BTRFS info (device sdc1): disk space caching is enabled
> [Thu Aug 15 08:47:42 2019] BTRFS info (device sdc1): has skinny extents
> [Thu Aug 15 08:47:42 2019] BTRFS error (device sdc1): parent transid verify failed on 229846466560 wanted 49749 found 49750
> [Thu Aug 15 08:47:42 2019] BTRFS error (device sdc1): parent transid verify failed on 229846466560 wanted 49749 found 49750
> [Thu Aug 15 08:47:42 2019] BTRFS error (device sdc1): failed to read block groups: -5

Extent tree corruption.

So if that's the only corruption, you have a very high chance to recover
most of your data.

Btrfs rescue can work, or you can try the experimental patches which
provides rescue=skip_bg mount option to allow you mount the fs RO and
receive your data (later is way faster than user space rescue)
https://patchwork.kernel.org/project/linux-btrfs/list/?series=130637

Also, for your dump super output, it doesn't provide too much info.

You would like to use -Ffa option for more info.
Also, you could also try that on all 3 devices, to find out which one
has lower generation.

Also, please provide the history of the corruption.
One generation corruptions is a little rare. Is sudden power loss
involved in this case?

Thanks,
Qu

> [Thu Aug 15 08:47:42 2019] BTRFS error (device sdc1): open_ctree failed
> 
> Output from 'btrfs check -p /dev/sdc1':
> 
> # btrfs check -p /dev/sdc1
> Opening filesystem to check...
> parent transid verify failed on 229846466560 wanted 49749 found 49750
> Ignoring transid failure
> ERROR: child eb corrupted: parent bytenr=229845336064 item=0 parent level=1 child level=2
> ERROR: cannot open file system
> 
> 
> 
> On 08/15/2019 10:35 +0800, Qu Wenruo wrote:
>>> 	
>>> 	
>>> 	On 2019/8/15 ??????2:32, Tim Walberg wrote:
>>> 	> Most of the recommendations I've found online deal with when "wanted" is
>>> 	> greater than "found", which, if I understand correctly means that one or
>>> 	> more transactions were interrupted/lost before fully committed.
>>> 	
>>> 	No matter what the case is, a proper transaction shouldn't have any tree
>>> 	block overwritten.
>>> 	
>>> 	That means, either the FLUSH/FUA of the hardware/lower block layer is
>>> 	screwed up, or the COW of tree block is already screwed up.
>>> 	
>>> 	> 
>>> 	> Are the recommendations for recovery the same if the system is reporting a
>>> 	> "wanted" that is less than "found"?
>>> 	> 
>>> 	The salvage is no difference than any transid mismatch, no matter if
>>> 	it's larger or smaller.
>>> 	
>>> 	It depends on the tree block.
>>> 	
>>> 	Please provide full dmesg output and btrfs check for further advice.
>>> 	
>>> 	Thanks,
>>> 	Qu
>>> 	
> 
> 
> 
> 


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