On Wed, Jan 20, 2010 at 06:14:02AM -0800, Dirk H. Schulz wrote: > Pasi Kärkkäinen schrieb: > > On Sun, Jan 17, 2010 at 02:47:00PM +0100, Dirk H. Schulz wrote: > > > >> 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" > >> > > > > Before freezing the GFS you should make sure the VMs are in consistent > > state, and the VMs have flushed their caches/buffers/disks. > > > That means calling > sync > echo 3 > /proc/sys/vm/drop_caches > inside the VM, right? Or is there anything more to do to flush everything? > > Dirk I would think the best way would be to actually pause the VM. If you snapshot a VM while it's running, even with the above, how can you guarantee an application won't do something on the VM right as the snapshot occurs? Ray -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
