On Wed, Oct 14, 2009 at 10:52:19AM -0700, nate wrote:
> James A. Peltier wrote:
>
> > Mounting a snapshot requires the generation of a new UUID for the file
> > system in order to be able to use it. Perhaps this is a XFS limitation,
> > but unlike ZFS they aren't immediately available. We need to perform this
> > action extensively to backup file systems and allow for quick data
> > recovery.
>
> Another side effect of snapshots and using LVM for example(applies
> to any vendor's block based snapshots), is you can't easily take
> a snapshot of an LVM-based file system, then mount that snapshot
> on the same system, LVM will bitch. I spent some time trying to
> play with dynamically changing the UUID in the volume group but
> gave up, too complicated for my needs, instead I just mount the
> snapshot on another system(or a VM with either Raw device mapping
> in VMware or a software iSCSI initiator on the guest).
>
> I've written a few scripts for things like mysql snapshots and
> Oracle snapshots over the years with my 3PAR array, using SSH
> and key-based authentication the interface is pretty easy, a single
> command to create a read-only snapshot, then another command
> to create a read-write (read-write snapshots must be children of
> read-only ones in the 3PAR world anyways). The process takes less
> than a second, and if I want to snapshot a dozen volumes at the
> same instant, still a single command and the array ensures all
> volumes are taken at the same point in time, very helpful for
> Oracle snapshots which can get messy if your dealing with
> multiple volumes and not having them all perfectly in sync
> with each other.
>
On Equallogic you can group your volumes, and snapshot the whole group.
So it's meant exactly for this purpose; your database tables, logs and indices
(and what not) are quaranteed to be snapshotted at the exact same time.
-- Pasi
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