[linux-lvm] Snapshot of an LVM snapshots?
Prashanth Radhakrishnan
shanth at cs.utah.edu
Thu Aug 24 06:54:35 UTC 2006
Hi LVM Gurus,
>From what I've read around, it is not possible to take a snapshot of an
LVM snapshot. Is this something that is worked upon currently as a future
enhancement? If not, why not?
To give you a background, we're working on a periodic (xen) VM
checkpointing project, using LVM for VM disk checkpointing. As we take
several snapshots of the same volume, the write throughput reduces
drastically. I conjecture this is because, for each write to the (base)
volume, each of the snapshots' mappings is checked to decide whether to
copy the blocks to the snapshot or not.
It seems that this can be helped by:
- taking a snapshot of the latest snapshot and having the writes go to
the new snapshot
or
- making LVM use only the latest snapshot for CoW as writes go to the base
volume.
Any suggestions/pointers greatly appreaciated.
thanks,
Prashanth
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