Drive unmountable FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF issue

Solution 1:

The partition disk2s5 has the wrong partition type. It should be 53746F72-6167-11AA-AA11-00306543ECAC instead of FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF!

To solve this boot to Macintosh HD (disk0s2/disk1), open Terminal and enter:

• to get an overview:

  diskutil list
  

  below I assume the external disk has the disk identifier disk2

  sudo gpt -r show /dev/disk2
  

• unmount disk2:

  diskutil umountDisk /dev/disk2
  

• remove the partition entry with the index 5 (and the type FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF):

  sudo gpt remove -i 5 /dev/disk2
  

• re-add the same partition entry but with the proper type:

  diskutil umountDisk /dev/disk2
  sudo gpt add -i 5 -b 781921784 -s 976562504 -t 53746F72-6167-11AA-AA11-00306543ECAC /dev/disk2
  

• the external file vault volume (disk2s5) should be mounted automatically and you will be asked for the password. If not, enter diskutil cs list and diskutil cs unlockVolume lvUUID (with lvUUID: the Logical Volume UUID inside the second Logical Volume Group)

Update because the Recovery HD partition was removed somehow:

• Remove all partitions:

  diskutil umountDisk /dev/disk2
  sudo gpt destroy /dev/disk2
  diskutil umountDisk /dev/disk2
  sudo gpt create -f /dev/disk2
  

• re-add all partitions one by one:

  sudo gpt add -i 1 -b 40 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk2
  sudo gpt add -i 3 -b 780390104 -s 1269536 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk2
  sudo gpt add -i 4 -b 781659640 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk2
  sudo gpt add -i 6 -b 1758484288 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk2
  sudo gpt add -i 8 -b 3631786896 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk2
  sudo gpt add -i 10 -b 3906701272 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk2
  sudo gpt add -i 2 -b 409640 -s 779980464 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk2
  diskutil umountDisk /dev/disk2
  sudo gpt add -i 7 -b 1758746432 -s 1873040464 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk2
  diskutil umountDisk /dev/disk2
  sudo gpt add -i 9 -b 3632049040 -s 274652232 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk2
  diskutil umountDisk /dev/disk2
  sudo gpt add -i 5 -b 781921784 -s 976562504 -t 53746F72-6167-11AA-AA11-00306543ECAC /dev/disk2
  

I have chosen a "non-sequential" adding of partitions to unmount disk2 less often!