I built a Windows Server 2008 / Exchange 2007 GeoCluster recently and a co-worker was nice enough to find this for me to answer some questions I had in regards to the file share witness/quorum.
When using the Node and File Share Majority mode, review the following recommendations for the file share witness:
• Use a Server Message Block (SMB) share on a Windows Server 2003 or Windows Server 2008 file server.
• Make sure that the file share has a minimum of 5 MB of free space.
• Make sure that the file share is dedicated to the cluster and is not used in other ways (including storage of user or application data).
• Do not place the share on a node that is a member of this cluster or will become a member of this cluster in the future.
•You can place the share on a file server that has multiple file shares servicing different purposes. This may include multiple file share witnesses, each one a dedicated share. You can even place the share on a clustered file server (in a different cluster), which would typically be a clustered file server containing multiple file shares servicing different purposes.
• For a multi-site cluster, you can co-locate the external file share at one of the sites where a node or nodes are located. However, we recommend that you configure the external share in a separate third site.
• Place the file share on a server that is a member of a domain, in the same forest as the cluster nodes.
•For the folder that the file share uses, make sure that the administrator has Full Control share and NTFS permissions.
•Do not use a file share that is part of a Distributed File System (DFS) Namespace.