So… Stood up some 2012R2 XA7.6 servers the other day, using PVS7.6 and cache in RAM with overflow to disk.
Then I saw that I had files in the WriteCache directory on the PVS server. WTF?
After some screwing around, I found the solution.
Apparently PVS can’t use a disk that is GPT, you must use MBR. Once I switched that and reformatted the disks, viola! Everything worked exactly as it should.