This is just for my home lab and I'm running ESXi off a USB stick. All datastores are on the NAS and there is no internal storage in the server. I previously upgraded using the ISO method from 5.5 to 6.0u1 without issue. However now when I put the 6.5u2 DVD in, it starts up and successfully loads 6.5.0, but it doesn't detect my USB drive as containing a VMFS partition. It just shows it as a device which is available for install. If I select "details", one of the attributes says "ESXi 6.0.0 detected", but when I proceed, it only gives me the option to install, not upgrade.
Any ideas what could be causing this and how to resolve it?