What is a “quorum disk” and how does it help MSCS provide high availability?
It’s a disk spindle that MSCS uses to determine whether or not another server is up or down. Technically, it’s a resource that can only be owned by one server at a time, and for which servers can negotiate for ownership. Negotiating for the quorum drive allows MSCS to avoid “split brain” situations where both servers are active and think the other server is down. (This can happen when, for example, the cluster interconnect is lost and network response time is problematic.) The use of a quorum resource is one of the sophisticated algorithms that Microsoft got by working with pioneers in clustering such as Digital and Tandem.
