Recently, I had to migrate a client's projects from one of their RAIDs to another. Now, you could tempt fate and use FCP's Media Manager to copy or move files but overall Media Manager is a laughable mess and I avoid it whenever I can.
In the process of pre-organizing all their files before the big copy/move I noticed that while launching and looking at random projects they were working on that many of them used the same media, but they were pulling the media from different places on the same RAID. Meaning, they had multiple copies of some of their media which was taking up a lot of room that otherwise could have been freed up. Since I'm a bit of an organizational freak and didn't want to spend more time than was necessary in copying about 4TBs of stuff around I decided to pair down their RAID by removing redundant files.
Now, there are ways to do this with the terminal and some arcane Unix commands which worked at first but scared the owner of the business when he walked in and saw me typing away furiously into the terminal. So, I showed him a more friendly way and explained what I was doing.
I had them buy a license to Tidy Up! which is a shareware app that basically does what a handful of terminal commands do but with a pretty interface.
It'll rummage through a drive or series of HD's or just folders and spit out a list of duplicate files. You can preview them, move them and trash them right from the app. I ran it a bunch of times, made some notes, tossed out a whole mess of files and then moved the remaining files to nicely organized folders then reconnected them in FCP, tested it by opening all their save files and taa daa, saved just over terabyte of space on their RAID. Yes, it was that bad.
So ,if you have a pile of HD's or aren't that organized you may want to give it a try just to see how much space you can save and how many redundant files you have. Go slow, take notes and don't empty the trash until you're sure. The cool thing about Tidy Up! is that right up until you empty the trash you can Restore every file to it's original location in case you make a mistake.
Then, I trashed all their render files to save even more room and time. Then, I sent them a huge invoice.