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[lvm-devel] snapshot in shared disk environment


Is it possible or is there on-going work to use snapshot in shared disk

In virtualization context, snapshotting is useful for quickly
creating a guest image from a template disk image.
(Fast creation and space efficiency with a cost of runtime performance)

LVM snapshot can be used for such a purpose, but there is a problem
if we are in shared disk environment:
  a) Clustered snapshot is not yet supported.
  b) Origin and snapshots are activated/deactivated as a whole set.
     We can't individually activate/deactivate different snapshots on
     different nodes.

a) might be ok.
A snapshot is accessed on a host at a time, not simultaneously on multiple
hosts. Also the origin is read-only.
So snapshot itself need not be cluster aware, I think.
If there are thousands of nodes sharing the disk, but only one of them
accesses the snapshot, clustered snapshot seems overkill.

I wonder whether we could relax the restriction in b) and allow individual
activation of snapshots.
Then, we can use snapshots in shared disk environment without clustered
snapshot support?

Jun'ichi Nomura, NEC Corporation

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