Partition type suddenly FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF, drive unmountable

You have to edit the partition table and modify the type of disk1s2 (and correct the type of disk1s3) to get your main data partition back and make Boot OS X invisible:

1. Log-in as admin

2. Open Terminal and enter

   sudo gpt -r show /dev/disk1
   

   to get an overview

3. Unmount disk1:

   diskutil umountDisk /dev/disk1
   

4. Remove partition 2 and 3:

   sudo gpt remove -i 3 /dev/disk1
   diskutil umountDisk /dev/disk1
   sudo gpt remove -i 2 /dev/disk1
   

5. Re-add the partition 2 and 3

   diskutil umountDisk /dev/disk1
   sudo gpt add -b 928144008 -i 3 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk1
   diskutil umountDisk /dev/disk1
   sudo gpt add -b 409640 -i 2 -s 927734368 -t 53746F72-6167-11AA-AA11-00306543ECAC /dev/disk1
   

The correct partition type of a Boot OS X partition is 426F6F74-0000-11AA-AA11-00306543ECAC (like a Recovery HD partition) and 53746F72-6167-11AA-AA11-00306543ECAC for a CoreStorage partition.

Update: gpt behaves strange because the partition table contains an MBR instead of an PMBR - the MBR has to be replaced by a PMBR:

• Reboot your Mac

• Open Terminal and enter

  sudo gpt -r show /dev/disk1
  

  to get an overview and all partition sizes/types

• rebuilding the GUID partition table and destroying the bogus MBR

  diskutil umountDisk /dev/disk1
  sudo gpt destroy /dev/disk1
  diskutil umountDisk /dev/disk1
  sudo gpt create -f /dev/disk1
  sudo gpt add -b 40 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk1
  sudo gpt add -b 409640 -i 2 -s 927734368 -t 53746F72-6167-11AA-AA11-00306543ECAC /dev/disk1       
  diskutil umountDisk /dev/disk2 
  diskutil umountDisk /dev/disk1
  sudo gpt add -b 928144008 -i 3 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk1
  diskutil umountDisk /dev/disk2
  diskutil umountDisk /dev/disk1
  sudo gpt add -b 929021952 -i 4 -s 39294976 -t EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 /dev/disk1
  diskutil umountDisk /dev/disk2
  diskutil umountDisk /dev/disk1
  sudo gpt add -b 968318976 -i 5 -s 8388608 -t 0657FD6D-A4AB-43C4-84E5-0933C84B4F4F /dev/disk1