[lvm-devel] snapshot in shared disk environment

[Jun'ichi Nomura]

Hi,

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


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?

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation