Missing Files

I've noticed that some video files that I'm pretty sure I had on my server's hard drive have gone missing. It could be that they weren't there to begin with, but I'm pretty sure they were. I'd like to run fsck, but I can't unmount the hard drive. I know there's a way to go about it with fstab, but I was really hoping for a quick and easy way to unmount the drive, even a script.