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Re: [Linux-cluster] GFS on SAN, does a quorum make sense?

On 5/5/05, Dan B. Phung wrote:
> Hello, I was wondering if a quorum makes sense when I have one underlying
> shared device.  My setup is this:
>            blade1 b2  b3  b4  b5  .....
>               \    |   |   |   |  |  |  /
>                [ fiber switch module ]
>                         |  |
>                   [FastT500/EXP500]
> and I want any blade to be able to access the storage at anytime.  right
> now I have my configuration such that each node has the number of votes
> equivalent to the quorum.  Does this make sense?  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.
> 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?
> regards,
> Dan

You could designate a single "master node" that had N+1 votes.

Anytime it was online and part of the cluster, and of the other nodes
could come and go as they please.

Unfortunately, if it ever goes offline, you lose all access to the
shared storage.

If you made your "master node" be a low-cost but reliable node that
had zero job responsibility besides being the master, it should be
able to stay up for very long periods of time.

It is similar to the concept most companies use for DNS servers.  Give
them a single simple job and they are very reliable and the job is
simple enough to run on a 486 for most small businesses.

Greg Freemyer
The Norcross Group
Forensics for the 21st Century

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