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 support enabling Symmetric Multiprocessing Fault Tolerance (SMP-FT) VMs when PFFT is set to 0 and Affinity is set to Preferred or Secondary. Virtual SAN does not support SMP-FT VMs on a stretched cluster with PFFT set to 1 or more.
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.