I went ahead and upgraded my PR4100 raid 10 from OS 3 to OS 5. It went smooth and no hiccups at all. When asked, I installed the recommend Plex app, but then had to download an updated OS 5 version from the Plex website to update that.
But it moved over all my data, libraries, metadata, databases, etc… So did not loose my custom collections / view history / custom metadata / graphics.
I did take the extra precaution before hand to backup all of my data and to use SSH to backup all of my Plex databases and settings. Here is a GREAT video to show step by step how easy it is to backup the Plex database & settings in case something happens (like the power goes out midway through the upgrade)
