[Info-vax] troubles with quorum disk

[Keith Parris]

On 1/7/2013 10:01 AM, Stephen Hoffman wrote:
> If you're aiming to survive the loss of one host (as I'd suspect), then
> set the quorum disk to three votes, and set the EXPECTED_VOTES to five
> on both hosts.

I have to agree with Ken.

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.

I think maybe Hoff ended up with n+1 instead of n-1 when recalling the 
formula here -- a simple one-bit (sign-bit) error. My gray-matter memory 
doesn't have parity, either.

Everything else was spot on, as always.