With Windows clustering, a quorum refers to an area of disk storage where all nodes
participating in the cluster can come to meet to decide on who controls what resources
(in a very nonpolitical manner, contrary to our ancient Roman friends). In technical
terms, a quorum is an area of storage on a shared disk, accessible by all servers involved
in this particular instance of clustering. The quorum is usually referred to as the quorum
database. Do not take this to mean that the quorum is a SQL Server database! It is a proprietary
storage structure used by Windows to house quorum data??”for example, node x
owns resource 1, node y owns resource 2, and so on. Without a quorum database, there
can be no clustering.
With a two-node configuration, the function of the quorum is quite simple. Only
one node can own a specific disk resource, so each node must be in agreement about
which resources each is controlling. This information is retained in memory when both
nodes are running, but it is also written to the quorum. Why? Let??™s say a node physically
fails. As soon as the operational node sees that the failed node isn??™t participating in the
quorum, it checks the quorum to determine if another node has control over disk
resources that it would normally control.
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