Plan and design your upgrade to be fail-safe. Before you attempt to upgrade vSAN, verify that your environment meets the vSphere hardware and software requirements.

Upgrade Prerequisite

Consider the aspects that might delay the overall upgrade process. For guidelines and best practices, see the vSphere Upgrade documentation.

Review the key requirements before you upgrade your cluster to vSAN 6.6.

Table 1. Upgrade Prerequisite

Upgrade Prerequisites


Software, hardware, drivers, firmware, and storage I/O controllers

Verify that vSAN 6.6 supports the software and hardware components, drivers, firmware, and storage I/O controllers that you plan on using. Supported items are listed on the VMware Compatibility Guide website at

vSAN version

Verify that you are using the latest version of vSAN. You cannot upgrade from a beta version to vSAN 6.6. When you upgrade from a beta version, you must perform a fresh deployment of vSAN.

Software upgrade

Verify that you have enough space available to complete the software version upgrade. The amount of disk storage needed for the vCenter Server installation depends on your vCenter Server configuration. For guidelines about the disk space required for upgrading vSphere, see the vSphere Upgrade documentation.

vSAN disk upgrade

Verify that you have enough capacity available to upgrade the disk format. If free space equal to the consumed capacity of the largest disk group is not available, with the space available on disk groups other than the disk groups that are being converted, you must choose Allow reduced redundancy as the data migration option.

For example, the largest disk group in a cluster has 10 TB of physical capacity, but only 5 TB is being consumed. An extra 5 TB of spare capacity is needed elsewhere in the cluster, excluding the disk groups that are being migrated. When upgrading the vSAN disk format, verify that the hosts are not in maintenance mode. When any member host of a vSAN cluster enters maintenance mode, the cluster capacity is automatically reduced. The member host no longer contributes storage to the cluster and the capacity on the host is unavailable for data. For information about various evacuation modes, see the Place a Member of Virtual SAN Cluster in Maintenance Mode.

Host data evacuation mode

Verify that you have placed the vSAN hosts in maintenance mode and selected the Ensure data accessibility or Evacuate all data option.

You can use the vSphere Update Manager for automating and testing the upgrade process. However, when you use vSphere Update Manager to upgrade vSAN, the default evacuation mode is Ensure data accessibility. When you use the Ensure data accessibility mode, your data is not protected, and if you encounter a failure while upgrading vSAN, you might experience unexpected data loss. However, the Ensure data accessibility mode is faster than the Evacuate all data mode, because you do not need to move all data to another host in the cluster. For information about various evacuation modes, see the Place a Member of Virtual SAN Cluster in Maintenance Mode.

Virtual Machines

Verify that you have backed up your virtual machines.


Consider the following recommendations when deploying ESXi hosts for use with vSAN:

  • If ESXi hosts are configured with memory capacity of 512 GB or less, use SATADOM, SD, USB, or hard disk devices as the installation media.

  • If ESXi hosts are configured with memory capacity greater than 512 GB, use a separate magnetic disk or flash device as the installation device. If you are using a separate device, verify that vSAN is not claiming the device.

  • When you boot a vSAN host from a SATADOM device, you must use a single-level cell (SLC) device and the size of the boot device must be at least 16 GB.

  • To ensure your hardware meets the requirements for vSAN, refer to Hardware Requirements for vSAN.

vSAN 6.5 and later enables you to adjust the boot size requirements for an ESXi host in a vSAN cluster. For more information, see the VMware knowledge base article at

Upgrading the Witness Host in a Two Host or Stretched Cluster

The witness host for a two host cluster or stretched cluster is located outside of the vSAN cluster, but it is managed by the same vCenter Server. You can use the same process to upgrade the witness host as you use for a vSAN data host.

Do not upgrade the witness host until all data hosts have been upgraded and have exited maintenance mode.

Upgrade vSAN hosts serially, not in parallel, to ensure an efficient upgrade process. Upgrade the witness hosts after the member hosts of the stretched cluster. VMware Update Manager upgrades the hosts serially.