There is no advantage to sparating Events and Projects on different drives. Total myth.
Way back in FCP 7 and previous versions, Larry Jordan explained media mangement with a two drive example. There was no technical reason for this, except Larry thought it was more clear for newbies to understand the concepts. I have discussed this in the past with him more than once.
Unfortunately, many newbies walked away thinking you HAD to put your project file on one drive, and the media on another. That was NOT what Larry thought he was explaining. But the myth continues today, and is completely wrong.
Keep Libraries (or Events & Projects) on a media drive, that is not the system drive, that is the ONLY advantageous set up.