We have a 4 node Hyper-V cluster running about 15 VMs. On none of them I have tested, can I inspect or edit VHDXs on running VMs. I get a permissions error of some kind when attempting to do so:
Given that the VMs are running, the hosts obviously have access to the files. I can browse to the location of the files and see them, and I can see currently Everyone has Full Control.
What else would prevent me from editing the disk given the above permissions?
The cause of my problem seemed to stem from the fact these VMs were being managed by WSFC (failover clustering), which prevented the Hyper-V manager from making these changes.
If I instead tried this process using failover clustering manager, I was able to expand the disk while the VM was online.