vSAN 7 Update 1 introduced a shared witness option for 2-node cluster configurations. The feature allows you to share one a witness host with up to 64 2-node vSAN clusters. This brings along greater optimization in terms of physical resources, manageability, design, and operations. This also means less time to perform upgrades when using shared vSAN Witness Hosts (instead of a Witness Host for every 2-node cluster). However, there are specific steps that must be followed when performing vSAN Witness Host upgrades. This article will give you some important recommendations and guidance on how to perform the upgrade in the most efficient way.
Recommended steps to follow when you want to perform a vSAN upgrade
- Verify your upgrade path and read the Release Notes
- Perform the vCenter Server Upgrade
- Upgrade with vSphere Lifecycle Manager in vSphere 7
- Finish the upgrade and consolidate witness Hosts
For a more detailed description of the 4 steps, listed above, see this article, which includes best practices on performing a vSAN upgrade.
In some cases, a health check stating the on-disk format version is out of date is displayed to prompt you to upgrade your on-disk format.
Keep in mind, there is a special consideration when it comes to 2-node clusters with a shared witness host. The on-disk format upgrade in a environment with multiple 2-node clusters and a shared witness should only be performed once all the hosts sharing the same witness are running the same vSphere/ version.
IMPORTANT: Do NOT upgrade the on-disk format of your disks until all hosts sharing the same witness are upgraded to the same vSphere version.
Example: Upgrading multiple 2-node clusters with a shared witness host from 7U1 to 7U2. 7U1 uses on-disk format version 13. 7U2 uses on-disk format version 14. The high-level steps to upgrade this environment are:
- Upgrade ALL 2-node physical hosts to 7U2 that use the shared witness host—do NOT upgrade the on-disk format version from 13 to 14.
- Upgrade the witness host to 7U2.
- Confirm all hosts are running 7U2.
- Upgrade the on-disk format to version 14 using the link in Skyline Health.
In case you do not follow the correct order and you attempt to roll out a disk format conversion with hosts running mixed versions, a network partition will take place and an error message will be displayed preventing you from finishing the disk format upgrade.
Again, make sure all the hosts using the shared witness host are running the same ESXi version before upgrading the on-disk format.
Once all the hosts are running version 7 U2, you can go ahead and successfully upgrade the disk format version from v13 to v14.