Re: recovering from "parent transid verify failed"

[Tim Walberg <twalberg@comcast.net>]

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
[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
>>	




-- 
+----------------------+
| Tim Walberg          |
| 830 Carriage Dr.     |
| Algonquin, IL 60102  |
| twalberg@comcast.net |
+----------------------+