Re: illegal snapshot, cannot be deleted

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-11-11 17:11, Vedran Vucic wrote:
> Hello,
>
> I use OpenSuse 13.2 on my Toshiba Satellite laptop. I noticed that I run
> out of disk space, checked documentation and I realized that there were
> many snapshots.  I used Yast Snapper to delete snapshots.
> I noticed that one snapshot  with number 748 could not be deleted.
> I entered terminal and after the command:
> snapper -c root delete 748
> I got message Illegal snapshot.
This sounds like some sort of issue with snapper, not BTRFS itself, but 
see below for some suggestions.
> I woudl like to delete it since it is old one.
> Please find details about my system as requested on your wiki page.
> uname -a
> Linux linux-jjcc.site 3.16.7-29-desktop #1 SMP PREEMPT Fri Oct 23 00:46:04
> UTC 2015 (6be6a97) i686 i686 i386 GNU/Linux
>
> btrfs --version
> btrfs-progs v4.0+20150429
>
> btrfs fi show
> Label: none  uuid: d6934db3-3ac9-49d0-83db-287be7b995a5
>          Total devices 1 FS bytes used 10.98GiB
>          devid    1 size 18.71GiB used 18.71GiB path /dev/sda6
>
> btrfs fi df /
> Data, single: total=15.19GiB, used=10.37GiB
> System, DUP: total=8.00MiB, used=16.00KiB
> System, single: total=4.00MiB, used=0.00B
> Metadata, DUP: total=1.75GiB, used=622.53MiB
> Metadata, single: total=8.00MiB, used=0.00B
> GlobalReserve, single: total=208.00MiB, used=0.00B
> Please find attached dmesg.log as requested.
>
> Please advise what have to do in order to delete snapshot that is reported
> to be illegal.
Have you tried running 'btrfs subvolume delete' on the snapshot?  You'll 
have to find the full path to it first of course, but that shouldn't be 
too hard.  Based on the lack of BTRFS error messages in the kernel log 
you posted, I'm pretty certain that this isn't an issue with the 
filesystem itself (although the filesystem doesn't look particularly 
healthy, see further below), so manually deleting the snapshot using the 
regular BTRFS commands should work just fine.  That said, you may also 
want to look into changing the config for snapper, as it has a 
ridiculously aggressive retention policy for snapshots by default, which 
tends to lead to excessive space usage on filesystems smaller than about 
250GB.

You may also want to look at running a balance on the filesystem, the 
numbers from btrfs fi show and btrfs fi df look somewhat worrying, 
you've got all the space on the disk allocated as chunks by BTRFS, but 
have a significant amount of empty space in those chunks.  Given that 
fact, ENOSPC issues are a very real possibility, and you'll probably 
have to run a series of partial balances to fix this (and it's important 
to do it before it becomes a visible issue also, because once you start 
getting ENOSPC errors, it is a lot harder to fix).  Try running a 
balance with '-dusage=0 -musage=0', then re-run repeatedly increasing 
the number for both arguments by 5 each time until you get to 50.  If a 
run complains about 'ENOSPC errors during balance', re-run it with the 
same number for -dusage and -musage.  If you end up re-running with the 
same value 3 times and keep getting the errors, then you're probably 
beyond the point of this being fixable, and should just recreate the 
filesystem (you do have backups, right?).  Otherwise, after finishing 
the run with '-dusage=50 -musage=50' successfully, run a full balance 
without the dusage and musage options.




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