I used to use USB memory sticks for local music storage with ROCK. The NUC fan was barely on.
Last week, I consolidated the set up by installing an internal 1TB SSD drive and moved the music library from the USB sticks to the SSD drive, after formatting the SSD drive with ROCK’s web interface. (The move was done by mounting both SSD drive and the USB sticks in a windows 10 PC and using “cut and paste” in windows)
Since, I can hear the NUC fan spins up once a while and the output air was warm to hot.
Depending on how you did it, Roon might be re analyzing your entire library. Did you follow the migration guides, because it is very easy to mix something up and have think all these files are new.
If Roon sees the contents of the new drive as “new”, then it will not only re-identify everything, it will redo the audio analysis. Audio Analysis uses a lot of CPU and maybe the reason behind the NUC being hotter.
You could go to Settings/Library and turn Audio Analysis to OFF and see if that cools things down. If so, then you can set OnDemand Audio Analysis to FAST, leaving the other OFF. This will analyze the track(s) before playing them, a slight delay once. OR, you can turn Audio Analysis ON when you are not playing anything, like sleeping, and then turn it OFF when you are using Roon for playback.
Yes, you can just wait and let it finish.
Also, be aware that you cannot backup Roon’s database to the internal drive, so you will still need an external drive or a network location as a place to backup the Roon database.
Do you do many edits? Or have a track you’ve played a lot? Check to see if the play counts and the edits are still there. If Roon is really seeing everything as “new” then that information will not be there.