Having trouble with Final Cut Pro disk space
.DV tends to be about 4MB/sec. So 5 hours is about 18,000 seconds, so you are looking at a capture of about 72000MB, 72G so you should be fine..

Are you sure the Capture Scratch disk is set properly? Sometimes it's set to the wrong drive you want to capture to.

Check Preferences if you are using FCP, if you are using FCPX it might be somewhere else, not sure how you set capture disks in FCPX..