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    SubjectRe: Inter-Kernel Communications (Multi Kernel Clusters)


    > There are some funny special cases that need to be considered. How
    > does your proposal handling failing components in the cluster? Imagine
    > a network failure that split your cluster in two parts, each fully
    > functional but unconnected to the rest. The so called split-brain
    > syndrome. Now each cluster half will continue processing and assumes
    > it is authoritive? Imagine a database system being split up into
    > two systems ...

    The VMS clusters handles this very nice by using a voting mechanism where
    each member has 0-N votes, and the sum of the votes must be a minimum of
    the "quorum" or "expected votes". If not, each cluster member will freeze
    the quorum has been reestablished. This algorithm is very simple yet very
    clever since it works - always !!!

    Member A (1 vote)
    Member B (1 vote)
    Member C (1 vote)

    = 3 votes

    Expected Votes = (3 (total) / 2) + 1 = 2 (Quorum)

    This gives that if one system leaves the cluster (network partitioned),
    then the
    remaining two nodes still has <Quorum> votes and can continue. The third
    node will NOT have enough votes (and does not see any other nodes) so it
    will freeze until the connectivity is reestablished.

    In a two-node cluster the same scheme can be achived by using a locally
    connected (or shared) disk as a voting member with 1 vote.


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      Last update: 2005-03-22 13:39    [W:0.018 / U:8.692 seconds]
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