Re: Virtualbox and btrfs superblock issue

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 29.07.24 16:03, Jérôme Bardot wrote:
> Hi,
> 
> Sorry if I post at the wrong place but  I didn't find an issue manager
> (like gitlab).
> (I also asking myself if a not already post but maybe before i subscribe)
> 
> So my issue :
> 
> On a windows host laptop and with a parrot vm with a btrfs and after a
> power failure the vm looks broken.
> At start the vm drop down to initramfs.
> When I try to mount from an iso (of the same os/version) i get following error :
> 
> mount -t btrfs /dev/sdc1 /media/user/to-rescue
> mount: /media/user/to-rescue: can't read superblock on /dev/sdc1.
>         dmesg(1) may have more information after failed mount system call.
> 
> and dmesg get following :
> [71283.615636] BTRFS: device fsid 70bf0953-3ee3-481f-8a7d-f7327c6fba67
> devid 1 transid 182616 /dev/sdc1 (8:33) scanned by mount (24156)
> [71283.627681] BTRFS info (device sdc1): first mount of filesystem
> 70bf0953-3ee3-481f-8a7d-f7327c6fba67
> [71283.627711] BTRFS info (device sdc1): using crc32c (crc32c-intel)
> checksum algorithm
> [71283.627725] BTRFS info (device sdc1): using free-space-tree
> [71283.639345] BTRFS error (device sdc1): parent transid verify failed
> on logical 26984693760 mirror 1 wanted 182616 found 182618
> [71283.642087] BTRFS error (device sdc1): parent transid verify failed
> on logical 26984693760 mirror 2 wanted 182616 found 182618
> [71283.645163] BTRFS warning (device sdc1): couldn't read tree root
> [71283.646224] BTRFS error (device sdc1): open_ctree failed
> 
> How can (if I can) I fix that kind of issue.
> (i did not create backup/btrfs snapshot)
> I get that issue on 2 similar setup / power failure and one with a xfs
> system too.
> 
> I'm really newbie with btrfs.
> 
> thx for your feedback.

This looks like the superblock didn't get written correctly, probably 
because of some kind of cache (volatile write cache in case of a disk, 
or some other cache in case of Virtualbox).

Ypu could try to mount with -o ro,rescue=usebackuproot and see if one of 
the backup roots is still valid.