Just a reminder to folks about a known glitch that got me in spite of knowing better. I copied the "Private" folder from my video cam to one of my hard drives. Later I opened FCPx and the hard drive that contained the Private folder disappeared from the Event Library after FCPx finished booting. I have quite a few folders on that hard drive and I spent an inordinant amount of time tracking the problem down in spite of knowing about the issue. I just didn't key in on that file quickly enough. I was in the midst of preparing to copy back my backup hard drive. Happily I was not concerned about losing any data or getting it back to working order. My external backup was seen perfectly as long as that Private folder was not at the root level.
I need to find the FCPx feedback link and bug report. This is NOT an elegant way for a program to deal with an issue like this. Similarly I recently opened FCPx when I had my mirror backup of my fcpx data hard drive online. Sometimes it warns me and then proceeds to work properly, other times is freezes and crashes if a mirror backup is online when FCPx opens. I've only goofed this a few times but it's easy to do and imho it's something they need to work on.
So..for anyone here doing a search on Missing Hard drive or something similar...be sure you don't have a duplicate hard drive mounted or any folder copied directly from your video camera at the ROOT level of a hard drive with an existing FCPx event folder.
As an aside I'd note that I had just recentlfy begun to use the Event Manager app and suspected it but didn't give in to the temptation to assume that the timing was a cause and effect. Strong urge though...