Stretched Cluster Design Considerations

Consider these guidelines when working with a Virtual SAN stretched cluster.

• Configure DRS settings for the stretched cluster.
  • DRS must be enabled on the cluster. If you place DRS in partially automated mode, you can control which VMs to migrate to each site.
  • Create two host groups, one for the preferred site and one for the secondary site.
  • Create two VM groups, one to hold the VMs on the preferred site and one to hold the VMs on the secondary site.
  • Create two VM-Host affinity rules that map VMs-to-host groups, and specify which VMs and hosts reside in the preferred site and which VMs and hosts reside in the secondary site.
  • Configure VM-Host affinity rules to perform the initial placement of VMs in the cluster.
• Configure HA settings for the stretched cluster.
  • HA must be enabled on the cluster.
  • HA rule settings should respect VM-Host affinity rules during failover.
  • Disable HA datastore heartbeats.
• Stretched clusters require on-disk format 2.0 or later. If necessary, upgrade the on-disk format before configuring a stretched cluster. See Upgrade Virtual SAN Disk Format Using vSphere Web Client.
• Configure the Number of failures to tolerate to one (FTT=1) for stretched clusters.
• Virtual SAN stretched clusters do not support symmetric multiprocessing fault tolerance (SMP-FT).
• When a host is disconnected or not responding, you cannot add or remove the witness host. This limitation ensures that Virtual SAN collects enough information from all hosts before initiating reconfiguration operations.
• Using esxcli to add or remove hosts is not supported for stretched clusters.