Tell HN: Back up your hard drive
First time I had a non-consecutive exception in my Mavericks main partition. I made a rescue but after upgrading a partition to Yosemite, linux wouldnt boot and refind wouldn't show up because of this new logical disk partition. It took like 4 hours to scp all my data to another computer, then reformat and set my environment up again.
2. Accidentally moved /usr/libexec instead of /usr/libexec/sharingd. With filevault on, this became a mega headache. Now my disk is partitioned in half (after fighting to decrypt the drive) and downloading yosemite to the partition. All because I modified a root directory path and put it back off by a directory. I am almost done fixing it now after another ~1.5 hours of install & config. Apple was awesome about allowing me support a month out of warranty but the "executive team" didn't seem to even know what a terminal was.
Tl;dr But seriously, image your computer, server, keurig coffee machine, whatever because when your data is as corrupt as your gov't, even they can't help you.