Definition : Number of elements that should be online for the cluster to be running .Each element is a vote
1. Cluster nodes (Full copy of cluster Database
2. Disk (Full copy of cluster Database)
3. windows shre ( partial copy of cluster Database)
-Cluster service makes sure to synch the cluster database between the cluster elements.
-When subset of the elements has Quorum ,means they can bring the cluster up.
Types of Quorum :
-Disk only : nodes that can communicate with the Disk , can create cluster ( single point of failure )( cluster database is only on the disk)
-Disk and Node Majority : Votes ( each node has a copy of the cluster database)
-Node Majority : Odd number
-Node Majority and share : Even number
Cluster Database :
-contains the number of memebers in the cluster to determine majority
-info about local database in each exchange 2010 node
-Registration info : about which NICs are for MAPI and Replication ( Exchnage 2010)