There are a few previous threads on this topic, mostly around the EX4 device. The short answer is that it doesn’t work, or doesn’t work right.
I recently purchased a My Cloud 3TB and found, to my surprise, that NFS was enabled but configured for anonymous access only. Given that the web management interface has nowhere to configure NFS and anything prior to NFSv4 would be a support nightmare for WD, it was a pleasant surprise that even anonymous NFS worked.
I did a bit of poking around the device after finding that we can enable SSH access and login as the root user. I didn’t change anything but I did start to look around.
The OS appears to be a modified version of an older Debian Linux distribution (anyone who can take advantage of that information probably already knows that). The version is sufficiently old that it is using init for system startup instead of systemd (which is good if you want NFS to work properly until the systemd folks sort things out).
As for NFSv4 …
The rpc_pipefs tool is missing. This tool is needed to create the communications link (named pipe) between the nfsd kernel module (that provides NFS server functionality) and rpc.idmapd (that provides name-to-id mapping). Without this tool, rpc.idmapd crashes on startup and you can’t map userids to names.
Either, WD accidentally removed the rpc_pipefs tool from their build or did so on purpose to disable NFSv4. Either way, it means we can’t get name-to-id mapping working and, sadly, can’t use NFSv4 to it’s full potential.
I can understand the oversight of the missing rpc_pipefs tool. I can also understand intentionally limiting NFS on these devices. These are consumer devices and the number of consumers who would want to make use of NFS is undoubted small compared to the market while at the same time possibly making a higher percentage of support calls due to NFS not working as expected. NFS prior to v4 is easy to set-up but relies on all systems having matching user-ids (which can be a challenge for many). By giving us anonymous NFS access, WD is showing some concern for us, so we should be happy they went that far.
NFSv4 can be a bit more tricky to setup than NFSv1, although not nearly as complicated as properly configuring NFSv3 (in my opinion). And I do wish they supplied us with the tools to enable full NFSv4 functionality even if it’s not a part of the web interface.