[linux-lvm] Is it possible to invalidate snapshots other than by overfilling?

Rob West robertfwest at gmail.com
Tue Jul 1 21:10:57 UTC 2008

Does anyone know of ways that snapshots can become invalid other than by
writing more to the origin than the COW device can hold?

The reason I ask is that we're having cases where a snapshot is becoming
invalid, but we are very skeptical that it is due to overfilling. The size
of the origin is 83G, and the size of the snapshot is 8G.

Here's what little we can tell from the logs:
1. Backup script creates a snapshot and starts copying data from it.
2. Before backup is finished (and thus, snapshot removed), the user reboots.
3. On reboot, we get the following message which seems to be normal for this
    kernel: device-mapper: table: 253:2: snapshot-origin: unknown target
4. About 23 hours later, the backup script tries to create the snapshot
again but fails b/c it's still there.
5. The backup script tries to clean up by removing the snapshot, but
lvremove causes a kernel oops because the snapshot is invalid. (We have
identified a potential patch for this, but are trying to figure out why the
snapshot was invalid in the first place.)

The kernel we're using is based off of Fedora 6 (2.6.18-1.2849).

Not sure whether it matters, but device-mapper is version 1.02.07 release
4.0.RHEL4 and lvm2 is version 2.02.06 release 6.0.RHEL4.

Thanks for any help,
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