Configure GFS in Single Node Instead of 3 minimum : HPE VME

[Nitin_NV]

Customer is having 4 Node Vmware cluster.. He has given 1 node for HPE VME .. He want to configure Single Node for HPE VME with GFS ... But error is coming as minimum 3 nodes supported

[Moto_PK]

Clarification on the Requirements:

Single node cluster: this is supported for testing and you can use it provided you don't need any HA .
Two node cluster: This is the minimum necessary for an HA cluster, BUT you need to add external, shared NFS storage for the cluster to be able to provide HA.
Three node cluster: This is the minimum node count for FC or iSCSI storage. The reason for it is that VME relies on GFS2 as the clustered Filesystem and this component requires 3 nodes.

So it is working as per the design. That is not an error message, rather a recommendation message to follow the best practice.

[mnavada]

The Global File System 2 (GFS2) file system allows several computers (“nodes”) in a cluster to cooperatively share the same storage. To achieve this cooperation and maintain data consistency among the nodes, the nodes employ a cluster-wide locking scheme for file system resources

For Cluster Redundancy & High Availability, A single node does not form a cluster.
At least two nodes are needed to provide failover and redundancy, ensuring that if one node fails, the other can still function.

GFS2 relies on DLM (Distributed Lock Manager) to maintain file system consistency across nodes.
DLM needs at least two nodes to function properly and manage concurrent access to shared storage.

A quorum mechanism is used in clusters to avoid split-brain scenarios (where nodes lose connection and act independently).

GFS2 is designed for a shared disk environment, meaning multiple nodes should access the same storage simultaneously.
With a single node, GFS2 provides no advantage over a local filesystem like ext4 or XFS.

A minimum of 3 nodes is often recommended to maintain quorum without dependency on a tie-breaker mechanism.

So, the WARNING message that reported is not an error message, rather a recommendation message to follow the best practice.

[Aqid]

A single node GFS2 absolutely does provide advantage over a local filesystem like ext4, namely, being able to prepare a node/SAN connection for allowing to add multiple hosts later. If we currently have a 2 node VMWare setup and we are N+1, we could reinstall 1 of the hosts with VME, connect them to the SAN and execute the migration. Due to the 3 host limitation that is not possible, even if we we're to add the hosts later. I would have to migrate to the 1 host on ext4 first, only to add 2 hosts later, then I can finally use GFS2 and I'd have to migrate from ext4 to GFS2. This limitation is single-handedly disqualifying VME for our entire install-base.