Re: Mount issue, mount /dev/sdc2: can't read superblock

[Chris Murphy <lists@colorremedies.com>]

On Thu, Dec 20, 2018 at 3:23 PM Peter Chant <pete@petezilla.co.uk> wrote:
>
> I managed to break my root partition today.  Playing with GPU
> passthrough to a second graphics card, unsuccessfully, I suspect lead to
> some lockups and/or unclean mounts.

Should not matter, in theory.


> I've Googled a bit and tried a number of things stopping just before
> 'btrfs check --repair'.  I'm running kernel 4.19.10.  I now have the
> latest version of btrfs-progs, but I do admit to 'having a go' with
> btrfs-progs 4.4.something from a Mint installation.
>
> I've tried btrfs-find-root - and got the following:
>
> btrfs-find-root /dev/sdc2
> Superblock thinks the generation is 793794
> Superblock thinks the level is 1
> Found tree root at 1113905790976 gen 7937947 level 1

For all supers to be off by nearly 50 generations is really weird.
That's a lot of transactions to happen, and fail, and only for the
most recent super commits to happen successfully.

What do you get for ' btrfs rescue super -v <dev>'? That's a read only
command, I wonder if all the supers are really valid. And if they are,
then I'd like to see 'btrfs insp dump-s -f <dev>' and see if there's a
log tree. And then also the output from 'btrfs check --mode=lowmem
<dev>' which is also read-only, don't use --repair unless a dev
recommends it.


-- 
Chris Murphy