At work we are planning to move toward RHEL CLustering and GFS. I just have a few general questions regarding GFS and clustering.

What is the minimum number of nodes in a cluster required?
Is fencing controlled by a separate box/ node, that is not communicating to GFS, or is it controlled by every node through Cluster Manager deamon?

GFS metadata lives in multiple copies on SAN, but how are the updates communicated between the multiple copies of metadata?

minimum number of nodes: 2 if you want to have a cluster. But it is advisable to use a quorum disk with two nodes.

Fencing control: Fencing is controlled by the majority amount of nodes in the cluster. They decide who gets fenced. By default always the lowest nodeid in the majority of the cluster gets the fencing request and therefore will do the fencing.

Metadata Updates of GFS: I'm not really into this but I would suppose that Metadata updates as all other updates to the gfs fs are protocted by transactions where all changes are logged into journal (at least the metadata changes to keep the fs constistent). Transactions are again protected by locks which would - in the default case - be made via dlm.

I hope that helps a bit.

It does, thanks.