A quorum service is a Windows operating system-based service deployed on a server distinct from the two servers (physical machines or PMs) running HA- or FT-protected virtual machines (VMs). Quorum servers provide data integrity assurances and automatic restart capabilities for specific failures in an everRun environment. Stratus strongly recommends using quorum servers, especially for SplitSite operation. You can configure an everRun PM pair with 0, 1, or 2 quorum servers.
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.
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 a potential split-brain scenario.
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