[Info-vax] Quorum strategy

[John E. Malmberg]

On 5/22/2019 3:44 AM, Marc Van Dyck wrote:
> Our production environment is made of 3 clusters of two members each,
> with a quorum disk. Each member has one vote, the quorum disk also,
> so expected votes is 3 and the quorum is 2.
> 
> Now, in our environment, one of the two cluster members is more
> important than the other because there are application parts that
> can run on this one only. We call this the primary member. The other one
> is the secondary member.
> 
> If case of system failure, if it is the secondary member that fails, we
> can just switch the applications that ran on it to the primary. The
> only price to pay will be a load more difficult to handle.
> 
> If the primary member fails and can't be restarted, we shut down the
> secondary too and restart it as primary. All data are on SAN storage,
> including the system disk. So it is just a matter of shutting down,
> change the boot flags, and restart.
<snip>
> 
> So, say that I give
> 
> - 2 votes on the primary member
> - 2 votes on the the quorum disk
> - 1 vote on the secondary member

The quorum disk is only needed if you need the secondary to survive for 
a period of time after the primary system fails, such as long enough for 
an orderly shutdown or do other diagnostics.

If you do not give equal votes to the two systems and quorum disk, when 
the primary system goes down, the secondary system will hang until 
either the primary rejoins the cluster, or you adjust the number of 
votes on the secondary via the console.

If this hang of the secondary is is acceptable, and your recovery is to 
crash it instead of an orderly shutdown, then your quorum disk is not 
doing anything useful in that configuration.  Essentially you have the 
same thing as 1 vote on the primary member, 0 votes on the secondary 
member, and no quorum disk.

Regards,
-John
wb8tyw at qsl.net_work