Upgrading vSAN is a multistage process, and you must perform the upgrade in a specific sequence.
Note:
The disk format upgrade is optional. If you use a previous disk format version, your vSAN cluster continues to run smoothly. For best results, upgrade the objects to use the latest on-disk format. The latest on-disk format provides the complete feature set of vSAN. To understand the vSAN upgrade process, see About the Virtual SAN Disk Format.
To upgrade the vSAN Cluster, see Upgrading the vSAN Cluster.