Introduction to High-Availability Clusters On Linux And Other Systems

The Microsoft cluster service supports 2-node and N-node configurations.
In a two-nodes configuration, SCSI reserve commands are used to handle I/O fencing.
If there is a "split brains", the formerly-active node will send a SCSI reserve every 3 seconds, while the formerly-passive node will send it every 5 seconds.
The first to manage to get SCSI reservation, becomes active.
in an N-node configuration, usually a Quorum disk is used to overcome 'split-brains' situations.
A quorum disk is used to handle a 'vote' for the active node. In order to win, a node must get (N/2)+1 votes. Thus, N is normally an odd number (e.g. 3).
Very commonly found in the field.
(Probably) works only with SCSI disk devices.

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