I struggled a bit to find out how to store my Photo Library on a NetGear ReadyNAS. SMB did not work, and SSHFS did not work either. I was unable to get AFP working too, and I saw that it was discouraged.
The solution was to mount the drive using NFS. Then I created a sparse bundle disk image with a Mac OS Extended (Journaled) partition with an Apple Partition Map, on the NFS mounted partition, and moved my Photos Library.photoslibrary onto the mounted image. Everything seems to be running fast and smoothly. (I'm on a gigabit LAN.)
It should be noted that I use ext4 for my NAS partitions, don't know if it matters.