| > "tie breaker" - what does this mean?
In the VAXcluster quorum scheme, VAX systems are given votes, and if a group of
nodes with a majority of the possible votes (quorum) can all talk to each
other, they can operate as a cluster. In the special case of 2 nodes, neither
can achieve quorum without the other; normally a quorum disk would be used to
"break the tie" in this case, or else a 3rd node can be added.
With an FDDI cluster spread between a couple of geographically-separated sites
(to hopefully survive a local disaster), quorum gets a little more complicated.
If one site is more important than the other, you can give it more votes and it
will act as the primary site; it can operate independently of the secondary
site, but the secondary site cannot operate independently of the primary site.
If both sites are equally important, or if you want operation at either site to
contine despite a disaster at one of the sites, you can't simply use a quorum
disk at once site or the other, since it would fall victim to the same disaster
that particular site suffers. Instead, a 3rd site is added to the FDDI ring as
a "tie-breaker" site; whichever of the two sites survives the disaster will be
able to talk with this site and continue cluster operations.
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