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Re: [Linux-cluster] Snapshotting GFS and freezing



Ray Van Dolson schrieb:
Hmm.. so snapshots with CLVM are possible nowadays?

No....

RH has stated (recently on this list) that patches exist to do it, but
it hasn't been a high enough priority for them to complete the work to
the point where it could be distributed to customers.

Okay then, how do you people out there with clusters that run virtual machines with live migration do backups of the virtual machines? I surely do not want to shut down the virtual machine to be able to copy the image safely away if I have live migration available.

At the moment there is only one way I can see. PLEASE prove me to be wrong.
Searching in RedHat's documentation I found that the problem is that lvm snapshots need exclusively allocated logical volumes. So I think the following
should be technically possible:
0. Start environment: the logical volume containing the images of the virtual machines uses gfs and is mounted on all relevant cluster nodes since VMs are running on several cluster nodes.
1. All VMs have to be migrated to one of the cluster nodes
2. On all other nodes, the gfs volume is unmounted
3. On the remaining node (where all VMs now run) the logical volume is bound exclusively with "lvchange -aey LOGICALVOLUME"
   (I hope this is possible without deactivating it first)
4. Now GFS on this volume is frozen: "gfs_tool freeze /mountpoint/of/local/volume"
5. Now the snapshot is generated and mounted
6. GFS is unfrozen again
7. The virtual machine images are copied off the snapshot
8. The snapshot is umounted und undone
9. The LV is activated on all cluster nodes again, GFS file system is mounted on all relevant cluster nodes again.
10. The virtual machines are migrated back to whereever they belong.

Now I would like to know:
- is that basically the correct approach?
- is there any better method to backup the virtual machines without shutting them down? - is anyone out there using the above steps regularly in a production environment?

Dirk


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