File Share Witness for MNS quorum 2-node clusters Dankwart Medger Trident Consulting S.L.

2 Majority Node Set Quorum - File Share Witness What is it? A patch for Windows 2003 SP1 clusters provided by Microsoft (KB921181)KB What does it do? Allows the use of a simple file share to provide a vote for an MNS quorum-based 2-node cluster In addition to introducing the file share witness concept, this patch also introduces a configurable cluster heartbeat (for details see MS Knowledge Brief) What are the benefits? The „arbitrator“ node is no longer a full cluster member. A simple fileshare can be used to provide this vote. No single subnet requirement for network connection to the „arbitrator“. One arbitrator can serve multiple clusters. However, you have to set up a separated share for each cluster. The „abitrator“ exposing the share can be a standalone server a different OS architecture (e.g. a 32-bit Windows server providing a vote for a IA64 cluster)

3 Majority Node Set Quorum - File Share Witness # cluster nodes# node failures App A App B App A App B \\arbitrator\share Get vote 0 (1 with MNS fileshare witness) App A Slide is animated

4 Majority Node Set Quorum - File Share Witness \\arbitrator\share1 MNS Private Property: MNSFileShare = \\arbitrator\share1 MNS Private Property: MNSFileShare = \\arbitrator\share2 \\arbitrator\share2 Cluster 2 Cluster1

5 File Share Witness - Installation & Configuration Installation Download the update from Install it on each cluster node A reboot is required !!! This will add a new private property to the MNS resource Configuration Set the MNSFileShare property to the share you created on the abitrator Command: cluster resource /priv MNSFileShare=\\servername\sharename Important: The account under which the cluster service is running must have read and write permission to the share After setting the property the MNS resource has to moved to activate the new setting. C:\>cluster. resource MNS /priv Listing private properties for 'MNS': T Resource Name Value S MNS MNSFileShare D MNS MNSFileShareCheckInterval 240 (0xf0) D MNS MNSFileShareDelay 4 (0x4)

6 File Share Witness - Prerequisits Cluster Windows 2003 SP1 & R2 (x86, x64, IA64, EE and DC) 2-node MNS quorum-based cluster Property will be ignored for >2 nodes Arbitrator OS requirements Windows 2003 SP1 or later MS did not test earlier/other OS versions even though they should work Server OS is recommended for availability and security File Share requirements One file share for each cluster for which the „arbitrator“ provides a vote 5 MB per share are sufficient The external share does not store the full state of the cluster configuration. Instead, the external share contains only data sufficient to help prevent split-brain syndrome and to help detect a partition-in-time Cluster Service account requires read/write permission For highest availability, you might want to create a clustered file share/file server

7 File Share Witness - additional parameters MNSFileShareCheckInterval This is the interval when the cluster service checks if it can write to the file share. If this verification fails, a warning event is logged in the system event log min: 4 sec default: 240 sec max: sec MNSFileShareDelay Delay in seconds that the cluster node (which does not currently own the MNS quorum resource) will wait until it tries to get the vote from the witness. This allows the current owner of the MNS quorum resource be preferred when trying to win the vote. min: 0 sec default: 4 sec max: 60 sec C:\>cluster. resource MNS /priv Listing private properties for 'MNS': T Resource Name Value S MNS MNSFileShare \\arbitrator\share D MNS MNSFileShareCheckInterval 240 (0xf0) D MNS MNSFileShareDelay 4 (0x4)

88 File Share Witness/Arbitrator - What does it mean for CLX? Remember: File Share Witness only works with 2-node clusters Abitrator Node requirementCLX with traditional MNSCLX with MNS using file share witness Cluster MembershipArbitrator is a full additional cluster memberand has full cluster configuration information. Arbitrator is external to the cluster and has only minimal cluster configuration information. Operating SystemSame Windows version as on other cluster nodes, e.g. if IA64 cluster, abitrator has to be IA64 server, as well. Can be different Windows versions, e.g. 32-bit fileshare witness (arbitrator) can serve 64-bit cluster. HardwareDetermined by the OS. Arbitrator could be a smaller, less powerfull machine than the main nodes Determined by the OS. Fileshare server could be a smaller, less powerfull machine than the main nodes. Due to the less strict OS requirements, the hardware selection is also more flexible. Multiple ClustersOne arbitrator node per cluster.One arbitrator can serve multiple clusters. Location3rd site Network requirementsSingle subnet. Should NOT be dependent on a network route (physically) through one DC in order to reach the other DC. Can be a routed network (different subnets). Should NOT be dependent on a network route (physically) through one DC in order to reach the other DC.