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Old 05-19-2010, 06:06 PM
Timm Essigke
 
Default workaround for LVM snapshot bug

Hi,



I found a workaround for the bug, but I am sure it should not be like
that (based on
http://tuxrx.org/content/cant-remove-open-logical-volume-error). To
reproduce:



% lvs



* LV***** VG***** Attr** LSize** Origin Snap%* Move Log Copy%* Convert

...

* work*** abraham -wi-ao* 10.00g



% ls -l /dev/mapper/abraham-work*

lrwxrwxrwx 1 root root 7 May 19 19:40 /dev/mapper/abraham-work ->
../dm-7



% lvcreate -s -nwork_snap -L100m /dev/abraham/work

* Logical volume "work_snap" created



% lvs

* LV******* VG***** Attr** LSize** Origin Snap%* Move Log Copy%* Convert

...

* work***** abraham owi-ao* 10.00g

* work_snap abraham swi-a- 100.00m work**** 0.01



% ls -l /dev/mapper/abraham-work*

lrwxrwxrwx 1 root root 7 May 19 19:38 /dev/mapper/abraham-work ->
../dm-7

lrwxrwxrwx 1 root root 8 May 19 19:38 /dev/mapper/abraham-work-real
-> ../dm-10

lrwxrwxrwx 1 root root 7 May 19 19:38 /dev/mapper/abraham-work_snap
-> ../dm-9

lrwxrwxrwx 1 root root 8 May 19 19:38 /dev/mapper/abraham-work_snap-cow
-> ../dm-11



% dmsetup remove /dev/mapper/abraham-work_snap

% dmsetup remove /dev/mapper/abraham-work_snap-cow

% lvremove /dev/mapper/abraham-work_snap

* Logical volume "work_snap" successfully removed



Now all traces of the snapshot are remove. If I only "dmsetup remove"
the snapshot, but not the "-cow" it persists and prevents future
snapshots.



I am not sure if it is a bug in lvm2 or rather in
kernel-image-2.6.32-trunk-* and* kernel-image-2.6.32-5-* together with
udev and dm. If I downgrade lvm2 from 2.02.62-1 to 2.02.39-7 the error
remains. Instead downgrading to 2.6.26 works as before.



Shall I report the bug against linux-2.6?



The sample uses the symbolic links because I modified
/lib/udev/rules.d/55-dm.rules according to message #44 of debian bug* #581593, but with the
block device the problem and solution is the same.



@Tim: I think you were right, that the bug is the same... Sorry!



I hope the workaround helps the maintainers to find the real source of
the problem.



Regards,



Timm
 

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