The other night, I decided to repartition the 3TB Fusion drive on my 27" iMac, and I did the most stupid thing ever. I stopped the partition process because it was taking too long. I was able to boot into my Mac OS, but there was 2.1 TB missing from the drive. Disk utility showed errors and repairing wouldn't work. The main partition was shown as having 800GB, but the second partition was missing. When in the partition part of disk utility, the 3.1TB drive was seen, but it showed 24KB free so I was unable to try a repartition. My partition table was totally screwed.
I called Apple care and after 2 hours on the phone, my issue wasn't resolved. Even after asking at the beginning of the call "is there a way via terminal to rebuild or refresh the partition table", they were unable to resolve my issue. I was asked if I could take it to a Genius bar and lucky for me there is an Apple store 15 minutes away, but unfortunately they were booked out for the next few weeks. They also suggested an Apple Authorised repairer, but I've dealt with them before and they were hopeless.
In the end I stumbled upon an article, via the apple discussion forums, on setting up a bootcamp on a 3TB Fusion drive and a few simple terminal commands solved my issue. I used the 3 below
-bash-3.2# diskutil coreStorage list (To get the Logical Volume Group GUID numbers etc)
-bash-3.2# diskutil coreStorage deleteVolume <Logical Volume> (Can't remember if this one was effective, but did it anyways)
-bash-3.2# diskutil coreStorage delete <Logical Volume Group GUID> (this solved my issue)
Even though I wasn't partitioning the drive for bootcamp, those bash command lines saved me, refreshing the partition table. I was able to repartition the drive via Disk Utility in internet recovery and installed from a time machine backup. Fusion drive working as I want it to. Just to note, my recovery partition was safe and was always showing up in disk utility.
The article:
http://dice.neko-san.net/2012/12/how-to-install-boot-camp-on-a-3TB-fusion-drive-mac/