Re: need help in a broken 2TB BTRFS partition

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

On 2021/10/16 05:01, Christian Wimmer wrote:
> Hi Qu,
>
> I hope I find you well.
>
> Almost two years that my system runs without any failure.
> Since this is very boring I tried make my life somehow harder and tested again the snapshot feature of my Parallels Desktop installation yesterday:-)
> When I erased the old snapshots I could feel (and actually hear) already that the system is writing too much to the partitions.
> What I want to say is that it took too long (for any reason) to erase the old snapshots and to shut the system down.

The slow down seems to be caused by qgroup.

We already have an idea how to solve the problem and have some patches
for that.

Although it would add a new sysfs interface and may need user space
tools support.

>
> Well, after booting I saw that one of the discs is not coming back and I got the following error message:
>
> Suse_Tumbleweed:/home/proc # btrfs check /dev/sdd1
> Opening filesystem to check...
> parent transid verify failed on 324239360 wanted 208553 found 184371
> parent transid verify failed on 324239360 wanted 208553 found 184371
> parent transid verify failed on 324239360 wanted 208553 found 184371

This is the typical transid mismatch, caused by missing writes.

Normally if it's a physical machine, the first thing we suspect would be
the disk.

But since you're using an VM in MacOS, it has a whole storage stack to
go through.

And any of the stack is not handling flush/fua correctly, then it can
definitely go wrong like this.


> Ignoring transid failure
> leaf parent key incorrect 324239360
> ERROR: failed to read block groups: Operation not permitted
> ERROR: cannot open file system
>
>
> Could you help me to debug and repair this please?

Repair is not really possible.

>
> I already run the command btrfs restore /dev/sdd1 . and could restore 90% of the data but not the important last 10%.

Using newer kernel like v5.14, you can using "-o ro,rescue=all" mount
option, which would act mostly like btrfs-restore, and you may have a
chance to recover the lost 10%.

>
> My system is:
>
> Suse Tumbleweed inside Parallels Desktop on a Mac Mini
>
> Mac Min: Big Sur
> Parallels Desktop: 17.1.0
> Suse: Linux Suse_Tumbleweed 5.13.2-1-default #1 SMP Thu Jul 15 03:36:02 UTC 2021 (89416ca) x86_64 x86_64 x86_64 GNU/Linux
>
> Suse_Tumbleweed:~ # btrfs --version
> btrfs-progs v5.13
>
> The disk /dev/sdd1 is one of several 2TB partitions that reside on a NAS attached to the Mac Mini like

/dev/sdd1 is directly mapped into the VM or something else?

Or a file in remote filesystem (like NFS) then mapped into the VM?

Thanks,
Qu

>
> Disk /dev/sde: 2 TiB, 2197949513728 bytes, 4292870144 sectors
> Disk model: Linux_raid5_2tb_
> Units: sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 4096 bytes
> I/O size (minimum/optimal): 4096 bytes / 4096 bytes
> Disklabel type: gpt
> Disk identifier: 942781EC-8969-408B-BE8D-67F6A8AD6355
>
> Device     Start        End    Sectors Size Type
> /dev/sde1   2048 4292868095 4292866048   2T Linux filesystem
>
>
> What would be the next steps to repair this disk?
>
> Thank you all in advance for your help,
>
> Chris
>