Before we dive in about the list of Stretched Cluster Storage Policy lets us understand what defines a stretched cluster. The VSAN Stretched Cluster is setup across two sites, with preferably an identical number of ESXi hosts distributed evenly between the two sites, and a witness host residing at a third site.
The data sites are connected via a high bandwidth/low latency link. The third site hosting the vSAN witness host is connected over a network to both active/active data sites.
Stretched Cluster configuration offers the ability to balance VMs between datacenters. The reason for opting to configure stretched cluster could be anything be it for disaster avoidance or for site maintenance all can be achieved with no downtime from a VM perspective as compute , storage and network are available across both sites. With addition to this stretched cluster also provides the ability to actively load balance resources between locations without any constraints when desired.
Note : There is one witness host in each vSAN Stretched Cluster , for deployments that manages multiple stretched clusters each cluster must have its own unique witness host. Shared Witness is not supported for stretched cluster configuration.
By Default when a VM is deployed on a vSAN stretched cluster it is deployed with a RAID-1 configuration. In previous versions of vSAN this was referred to as primary failures to tolerate.
List of all different Stretched Cluster VM Policies options ( Failure to Tolerate Polices ) :
Terminology used here is "Site disaster tolerance " And " Failure to tolerate" .
Site Disaster Tolerance - None - standard Cluster.
Site Disaster Tolerance - Host mirroring - 2 node cluster
Site Disaster Tolerance - Site Mirroring - stretched Cluster
Site Disaster Tolerance - None - keep data on preferred (stretched Cluster )
Site Disaster Tolerance - None - keep data on secondary (stretched Cluster )
Site Disaster Tolerance -None - Stretched Cluster
Failure to tolerate - No data redundancy
Failure to tolerate - No data redundancy with host affinity
Failure to tolerate - 1 Failure -RAID-1
Failure to tolerate - 1 Failure - RAID-5
Failure to tolerate -2 Failure - RAID-1
Failure to tolerate -2 Failure - RAID-6
Failure to tolerate -3 Failure -RAID-1
ESA VS OSA Policy Comparing :
Reference Document :
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