From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jun'ichi Nomura Date: Tue, 05 Apr 2011 19:23:20 +0900 Subject: snapshot in shared disk environment Message-ID: <4D9AED98.1080900@ce.jp.nec.com> List-Id: To: lvm-devel@redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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