A quorum service is a Windows operating system-based service deployed on a server distinct from the two servers (physical machines or PMs) of
Quorum servers ensure the integrity of VMs against multiple network failure scenarios, including split-brain, and provide for unattended startup of VMs after specific failures. Quorum server communication occurs via the management network.
Quorum servers are particularly important in SplitSite configurations. Best practice for SplitSite is to place a preferred quorum computer in a third facility and an alternate quorum computer in a fourth facility. However, you can also place the alternate quorum service computer with the preferred quorum computer and still obtain satisfactory service. See SplitSite Configurations for additional information.
If only two sites are available (thereby preventing the best practices configuration described above) and if one PM goes down and the surviving PM is unable to communicate with the quorum server (for example, because it is on the same site as the down PM), the VMs at the surviving site are automatically shut down to avoid running in split-brain.
Related Topics
Creating a SplitSite Configuration, which discusses quorum servers
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