[Linux-cluster] nolock and dlm nodes in the same cluster

[Jeff Sturm]

> -----Original Message-----
> From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com]
> On Behalf Of Steven Whitehouse
> 
> There is no harm in unmounting the cluster filesystem on all nodes and
then mounting
> it on exactly one node with lock_nolock to back it up. The only issue
is that you have to
> be very careful in the commands that you issue in order to be certain
that it has not
> been left accidentally mounted on one of the cluster nodes.

The obvious downside is that the GFS volume cannot be used at all during
the lock_nolock mount/backup.

Using a SAN that supports LUN snapshots, there is another way to get a
backup.  You can:

1. Freeze the GFS volume
2. Create a snapshot
3. Unfreeze GFS
4. Mount the snapshot with lock_nolock
5. Perform a conventional backup of the mounted snapshot

The first three steps should complete very quickly, minimizing downtime.
Steps 4 and 5 are performed on the snapshot only and do not disrupt the
original volume, nor does this result in increased dlm traffic.  The
only performance impact may be from increased block I/O from the SAN
during the backup.

-Jeff