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Physical and virtual Windows Server failover clusters and Hyper-V clusters support a Microsoft quorum witness. A witness is a voting member that helps determine quorum for surviving server nodes when some nodes in a failover cluster or Hyper-V cluster become isolated or go offline.
Note: Metro Volume witness and Microsoft quorum witness function independently. They have no awareness of each other.
It is a best practice to configure a Microsoft quorum witness whenever you need a tie-breaking vote for surviving server nodes to achieve quorum if there is an outage. If your failover cluster or Hyper-V cluster (local or stretched) has an even number of server nodes, configure a quorum witness to optimize resiliency as a best practice. However, a Microsoft quorum witness is not required.
In a Metro Volume configuration, a Microsoft quorum witness is an important component that optimizes the resiliency of your clustered Microsoft environment. Microsoft provides several witness options.
The optimal quorum configuration for clustered Microsoft environments on Metro Volume is a file share witness or cloud-based witness. The witness must have a reliable low-latency connection to all nodes in the cluster.
If you have a stretched cluster, place the file share witness at a third site (or configure a cloud-based witness) to avoid site bias. Site bias can cause an unintended outage if a file share witness is not placed at a third site.
For example:
Remedy: Place the Microsoft file share witness at a third site (Site C). Given the same scenario, the surviving node at Site B (one vote) and the file share witness (one vote) can achieve quorum (two votes) and stay online.
If a third site is not available for a file share witness, place the witness at the primary (preferred) site.
You can also configure a disk as a quorum witness. A disk witness is less resilient than a file share witness if you have a stretch-cluster configuration over metro distance. It is not possible to place a disk witness at a third site.
Note: Hyper-V guest VMs configured to use HA with Metro Volume should use shared virtual hard disks on a CSV. Use of in-guest iSCSI or virtual Fibre Channel (vFC) to achieve HA is not recommended. Use of pass-through disks is also not recommended except for temporary or specific use cases. To learn more about direct-attached and pass-through disks, see the Dell PowerStore: Microsoft Hyper-V Best Practices white paper on the Dell PowerStore Info Hub.