Can I run GFS in a 2-node cluster?

Yes. It is possible to use the Global File System (GFS) on two-node clusters on Red Hat Enterprise Linux releases 3, 4 and 5.

GFS depends on a lock manager, and different versions of Red Hat Enterprise Linux provide different lock managers:

• Red Hat Enterprise Linux 3: gulm

• Red Hat Enterprise Linux 4: gulm and dlm

• Red Hat Enterprise Linux 5: dlm

dlm is a distributed lock manager; therefore if one of the machines on the cluster is fenced, the lock operations continue normally.

On the other hand if gulm is used as the lock manager, it is only possible to have 1, 3, 4 or 5 lock managers in a cluster. Therefore in a two-node cluster with gulm, only one of the nodes is the lock manager: if this server is fenced, or becomes unavailable, the other node will not be able to perform lock operations. In this case GFS will not be accessible, and a full reboot of the cluster will be necessary to restore proper operation.

Because of this limitation it is strongly recommended to use dlm as the lock manager with two-node clusters.

For additional information about Red Hat Global File System, visit http://www.redhat.com/software/rha/gfs/ .