I hate NAS’s for music storage. I know that some people like them/need them, and we do support them, but I wouldn’t use one for Roon (or any software trying to manage 50-100k+ music files) for myself, regardless of library size.
They don’t support real-time watching for file changes very well, scanning them over the network takes 10-20x (or more) as long as a local disk. Because they don’t support filesystem watching very well, you pretty much have to scan the whole folder tree periodically to avoid missing changes.
Also, because networking is in the mix, there’s a whole litany of extra broken states they can get into, ways they can confuse the OS or the software, and weird behaviors that they can exhibit. Performance varies greatly from product to product, and sometimes the performance can be so bad that it causes major behavioral problems.
On some networks, or with some NAS’s, the connection to the filesystem bounces up and down several times a day, or more often, triggering Roon to re-scan the folder tree too many times.
With a large library, sometimes you can end up with Roon spending a decent fraction of the time scanning over the NAS for changes because the connection is bouncing up and down or just because it takes so long to walk the folder tree that the periodic scan every few hours (frequency is configurable) turns into Roon doing work a serious fraction of the time just to keep tabs on your files.
I keep my music on a USB drive hanging off of a ROCK-based NUC. It’s something I never have to worry about, and I like it that way.
I do use a NAS for a backup copy/archive of the music, and for some other stuff like video streaming where the much lower file count makes most of the disadvantages disappear.