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VMware vSAN upgrade best practices (2146381)

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This article describes prescriptive best practices for upgrading vSAN clusters


Successful vSAN cluster upgrades depend on both prerequisite steps to prepare the cluster for upgrade as well as adherence to certain recommendations during the upgrade process.

Before starting a vSAN Cluster upgrade

Before starting the vSAN upgrade process, ensure that the following requirements are met:

  1. The vSphere environment is up to date:

    • The vCenter Server managing the hosts must be at an equal or higher patch level than the ESXi hosts it manages.
    • All hosts should be running the same build of ESXi before vSAN cluster upgrade is started.

      • If the ESXi host versions are not matched, the hosts should be patched to the same build before upgrading.

  2. All vSAN disks should be healthy

    • No disk should be failed or absent
    • This can be determined via the vSAN Disk Management view in the vSphere Web Client

  3. There should be no inaccessible vSAN objects

    • This can be verified with the vSAN Health Service in vSAN 6.0 and above, or with the Ruby vSphere Console (RVC) in all releases.

  4. There should not be any active resync at the start of the upgrade process.

    • Some resync activity is expected during the upgrade process, as data needs to be synchronized following host reboots.

  5. Ensure that there are no known compatibility issues between your current vSAN version and the desired target vSAN version. For information on upgrade requirements, see vSAN upgrade requirements (2145248).

    • If required, update the vSAN cluster to the required build before undertaking the upgrade process to avoid compatibility concerns.

ESXi Host preparation

  • Ensure you choose the right maintenance mode option. When you move a host into maintenance mode in vSAN, you have three options to choose:
    • Ensure availability
      If you select Ensure availability, vSAN allows you to move the host into maintenance mode faster than Full data migration and allows access to the virtual machines in the environment.
    • Full data migration
    • No data migration
      If you select No data migration, vSAN does not evacuate any data from this host. If you power off or remove the host from the cluster, some virtual machines might become inaccessible.
  • Exit maintenance mode and resync
    • When the ESXi host is upgraded and moved out of maintenance mode, a resync will occur. You can see this through the web client.
    • Ensure this is complete before moving onto the next host. A resync is occurring as the host that has been updated can now contribute to the vSAN Datastore again. It is vital to wait till this resync is complete to ensure there is no data loss.

After starting a vSAN Cluster upgrade

After beginning the upgrade process, there are a few items to keep in mind:

  1. Do not attempt to upgrade a cluster by introducing new versions to the cluster and migrating workloads.

    • If introducing new hosts, ensure that they are of the same initial version and upgrade them along with the rest of the cluster.

  2. If you are adding or replacing disks in the midst of an upgrade, ensure that they are formatted with the appropriate legacy on-disk format version, if applicable. For more information, see How to format vSAN Disk Groups with a legacy format version (2146221).

    Failure to adhere to these best practices may result in one or more of the following issues:
    • Unexpected network partitions
    • Unexpected loss of data availability
    • vSAN cluster instability

    See Also

    Update History

    04/21/2017 - Added vSAN 6.6 to Products

    Request a Product Feature

    To request a new product feature or to provide feedback on a VMware product, please visit the Request a Product Feature page.


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