KB.921181 and "File Share Witness"

KB out yesterday (KB.921181) covers the introduction and details about the new “File Share Witness” quorum model. This is an improvement to the original MNS design that allows a read/write file share to serve as the “voter” for quorum status, eliminating the need for a third (or, at least, “odd-number”) node as voter. This new feature helps pave the way to more simplified and effective MNS clusters for use by the Cluster Continuous Replication feature of Exchange 2007 (pre-release documentation, but this section looks pretty complete).

This feature is released as a public hotfix (linked from the KB) to either Windows 2003 SP1 or Windows 2003 R2.