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[linux-lvm] LVM and inactive snapshots.



Hi,

It seems both LVM 0.8 and 0.9 don't address snapshots running out of
reserved space very well.  From experience using it here's what I'm
seeing.

When a snapshot runs out of reserved space, lvm deactivates the snapshot
and cleans up it's allocation units it was using for it.  It still leaves
the snapshot volume device around as well and if the snapshot was actively
mounted, it remains mounted.  Keep in mind after the snapshot has gone
inactive, the dataset image it is portraying is NOT the same as it was
prior, viewing it in inactive state seems to show the exact same data that
the source volume contains, ie. it's a pointer back to source volume.

Given the above I'm curious as to how others view this behaviour.  I'm
thinking along the lines of:  If the snapshot goes inactive and it's
portrayal of the filesystem is no longer valid it should go away. Go away
meaning, if an inactive snapshot volume is currently mounted possibly we
should forcefully unmount it as well as cleaning up it's device node
entries and removing it as a block device.

Does that seem proper?

I suppose the ideal here is that you should never run out of reserved
space though, and if you were DEPENDING on that snapshot and you did run
out of reserved space, well, I assume you're just completely screwed in
that case. :)



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