[Linux-cluster] GFS on SAN, does a quorum make sense?
lhh at redhat.com
Fri May 6 16:42:30 UTC 2005
On Thu, 2005-05-05 at 18:49 -0400, Dan B. Phung wrote:
> From my understanding,
> the quorum/voting procedure is to prevent split-brain scenarios where two
> nodes coming up for the first time might try to form two separate clusters
> of the same name, which will cause data corruption. How would I prevent
> that, while still allowing any one node, even by itself, to access the
> storage media.
It's not to prevent two nodes: it's to prevent "less than a majority" of
the nodes (votes really) from forming their own cluster.
What you're trying to do is exactly what the algorithm is designed to
Consider a case where any one node can become quorate (by itself) in an
N-node cluster. If you unplug the network cables on each node and start
up the cluster software on all N nodes, you'll end up with an N-way
split brain! I think that is probably not a good thing.
You can do it manually by adjusting cman_tool's expected votes down to a
small number while doing a one-node boot, but please ensure the rest of
the cluster is down before doing so.
> Another use of the quorum is for distributed disks in the case of a node
> failure the I/O to that disk is fenced. Is that correct?
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