[Info-vax] Quorum strategy

[Marc Van Dyck]

Hans Bachner explained :
> John E. Malmberg schrieb am 22.05.2019 um 15:13:
>> 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.
>>
>> [snip]
>
> With the vote distribution described by Marc, imho the secondary system will 
> happily continue to run as long as it has access to the quorum disk even if 
> the primary node goes down.
>
> Hans.

Which is indeed what we want to achieve. It's better for us to shutdown
the secondary in an orderly fashion, at a time of our choosing, rather
than have it crash abruptly.

-- 
Marc Van Dyck