I'm trying to get stuff off of my mergerfs pool that doesn't need to be there so I can unmount disks as needed when I need to replace. I'm trying to use lsof but it's showing nothing being accessed. That would be fine except I have my living room Kodi running media that is shared via nfs from that server and directory. Either it isn't showing as opened because of nfs it's all being loaded into the buffer that I don't see it being accessed.

Is there another way to list who and what files are being accessed at any given moment over nfs?

Normally lsof is pretty good, but you could also try https://linux.die.net/man/1/fuser, maybe some of the *top cmds like iotop, iftop, ftop ....

Of course you can always dig into /proc, but that's a bit drastic.