Stretched clusters extend the vSAN cluster from a single data site to two sites for a higher level of availability and intersite load balancing. Stretched clusters are typically deployed in environments where the distance between data centers is limited, such as metropolitan or campus environments.

You can use stretched clusters to manage planned maintenance and avoid disaster scenarios, because maintenance or loss of one site does not affect the overall operation of the cluster. In a stretched cluster configuration, both data sites are active sites. If either site fails, vSAN uses the storage on the other site. vSphere HA restarts any VM that must be restarted on the remaining active site.

Configure a vSAN cluster that stretches across two geographic locations or sites.

Prerequisites

  • Verify that you have a minimum of three hosts: one for the preferred site, one for the secondary site, and one host to act as a witness.

  • Verify that you have configured one host to serve as the witness host for the stretched cluster. Verify that the witness host is not part of the vSAN cluster, and that it has only one VMkernel adapter configured for vSAN data traffic.

  • Verify that the witness host is empty and does not contain any components. To configure an existing vSAN host as a witness host, first evacuate all data from the host and delete the disk group.

Procedure

  1. Navigate to the vSAN cluster in the vSphere Web Client.
  2. Click the Configure tab.
  3. Under vSAN, click Fault Domains and Stretched Cluster.
  4. Click the Stretched Cluster Configure button to open the stretched cluster configuration wizard.
  5. Select the fault domain that you want to assign to the secondary site and click >>.

    The hosts that are listed under the Preferred fault domain are in the preferred site.

  6. Click Next.
  7. Select a witness host that is not a member of the vSAN stretched cluster and click Next.
  8. Claim storage devices on the witness host and click Next.

    Claim storage devices on the witness host. Select one flash device for the cache tier, and one or more devices for the capacity tier.

  9. On the Ready to complete page, review the configuration and click Finish.

 

You can change the witness host for a vSAN stretched cluster.

Change the ESXi host used as a witness host for your vSAN stretched cluster.

Prerequisites

Verify that the witness host is not in use.

Procedure

  1. Navigate to the vSAN cluster in the vSphere Web Client.
  2. Click the Configure tab.
  3. Under vSAN, click Fault Domains and Stretched Cluster.
  4. Click the Change witness host button.
  5. Select a new host to use as a witness host, and click Next.
  6. Claim disks on the new witness host, and click Next.
  7. On the Ready to complete page, review the configuration, and click Finish.

 

You can configure the secondary site as the preferred site. The current preferred site becomes the secondary site.

Procedure

  1. Navigate to the vSAN cluster in the vSphere Web Client.
  2. Click the Configure tab.
  3. Under vSAN, click Fault Domains and Stretched Cluster.
  4. Select the secondary fault domain and click the Mark Fault Domain as preferred for Stretched Cluster icon ().
  5. Click Yes to confirm.

    The selected fault domain is marked as the preferred fault domain.