Despite the number, vSphere 6.5 does not represent a minor release of vSphere 6.0 but a new major release (the same considerations were possible with vSphere 5.0, 5.1, and 5.5). For this reason, you have to plan carefully whether to upgrade and how to upgrade. Finally, with vSphere 6.5 Update 1, it is possible to upgrade from vSphere 6.0 Update 3 (this was not supported in the previous version of 6.5).

There are several changes but also new features and scalability properties that make vSphere 6.5 interesting for new environments, but also for existing customers.

The main consideration to make with regard to the upgrade is that each new product (it does not matter whether it is a major or a minor release) brings new features, new code, and potentially maybe also new bugs (and the history of vSphere 5.1 and 6.0 has demonstrated that early adopters came across some issues). Of course, upgrading might also fix some existing bugs. But the maturity of a new release might not be the same as the previous versions. So, before upgrading, evaluate the new release by first using it in a dev or test environment or wait a few months to see the first feedback from the community and reported issues, and how and when they have been solved. Some prefer to wait for the first Update 1 version and, finally, it is here. To be honest, the code of the initial 6.5 release already seemed to be more mature than that of version 6.0 in its infancy.

You also have to consider all third-party code, included drivers or services, and kernel modules (for example, PernixData FVP is not compatible with 6.5) or switch extensions (after vSphere 6.5 Update 1, customers using third-party virtual switches such as the IBM DVS 5000v, HPE 5900v, and Cisco Nexus 1000v will need to migrate off of those switches prior to upgrading to any future release), vCenter plugins or integration with external software, for example, backup products. For third-party switches see KB 2149722—Discontinuation of third party vSwitch program at https://kb.vmware.com/kb/2149722.

Remember also that vSphere may be just a foundation of a bigger solution and architecture (as described before); in this case, you have to check every piece of software and hardware to match the compatibility and supported version.