[Info-vax] troubles with quorum disk

[Michael Moroney]

Keith Parris <keithparris_deletethis at yahoo.com> writes:

>QDSKVOTES=3 would indeed allow the survival of one host in a 2-node 
>cluster, but then so would any value of QDSKVOTES greater than zero. 
>However, any value over 1 makes the quorum disk into a single point of 
>failure for the cluster.

>The rule of thumb is: if you want to be able to boot a cluster with any 
>single node by itself up to as many as all the nodes, and never want to 
>worry about quorum, and you also don't want the quorum disk itself to 
>become a single point of failure, then set the quorum disk's votes to 
>one less (n-1) than the number of votes from the VMS systems. This 
>allows the cluster to survive loss of the quorum disk as long as all the 
>VMS nodes are present.

That is correct.  If you have a cluster with n nodes and you want it to
be able to run with any combination of the nodes (from 1 to all), set
EXPECTED_VOTES to 2n-1, each node to 1 and the quorum disk to n-1.
For the trivial case of a 2 node cluster, it becomes 1 vote each.

The quorum disk isn't a single point of failure, but it almost is.
The cluster can continue without it _only_ if all nodes are present.
(and you can't shadow the quorum disk)