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

[Sven Karlsson]

G'day,

We have a GFS2 cluster on a fibre-SAN with three machines, of which
one machine is used for remote backups.

The cluster contains a lot of small files, and the backup operation
takes about a day to complete. When investigating, we found that the
major performance bottleneck was the file locking operations. We
stopped the cluster and mounted the backup-node with the lock_nolock
option, and now backups were blazing.

After careful consideration of the nolock-warning in the documentation
(i.e. corruption and kernel panics may happen), I wonder if that is
still the case if spectator mode is used?

Or is there some other options that are available? The files will not
be modified by the other nodes during this time, so there is no actual
need for file-level locking... but perhaps the DLM is also handling
meta-data and other locking that is necessary and it is therefore not
possible to use nolock?

/Sven