[Linux-cluster] Quorum question

Patrick Caulfield pcaulfie at redhat.com
Wed Dec 21 11:20:53 UTC 2005

Bowie Bailey wrote:
> Graham Wood <mailto:gwood at dragonhold.org> wrote:
>>>Can I just drop the "two_node" definition for a 3-node cluster to
>>>force it to keep running with only one node?
>>If you're looking at GFS, then this arrangement is almost definitely
>>going to fry the data in the partition - which will take the system
>>down for you permanently.
>>Imagine that the 3 nodes lose communication (but all three are still
>>running) - they're all going to reply the logs from the other two, and
>>then start writing to the shared filesystem as if they were the only
>>ones in the cluster.
>>Which will corrupt the GFS very quickly.
> Isn't that what fencing is supposed to take care of?  Maybe I'm not
> understanding how this all works together.

No, because fencing has to be done by one of the cluster nodes. And the
cluster must be quorate to fence another node - otherwise it could be an
isolated node fencing the valid part.

> What I will have is three nodes.  Two that actively use the data in the
> shared storage and one node that handles backups.
> The backup node is not critical and could be down at any time for a
> number of reasons.  I want to make sure that if the backup node is down
> and one of the other nodes crashes, that the one remaining node will
> continue to be able to access the data in the GFS.



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