Under certain circumstances a deleted external HFS+ encrypted volume can be recovered after the disk has been formatted to a FAT32 volume:
If nothing has been written to the FAT32 volume those parts shouldn't be overwritten.
To recover the encrypted volume you have to use Terminal and do some math.
- Detach any external drive except the mal-formatted one
Open Terminal and enter:
diskutil list
to get an overview and the disk identifier of the external disk. Below I assume the disk identifier is disk1
- Make a backup of the whole disk with
sudo dd if=/dev/disk1 of=/Volumes/BackupVolume_Name/disk1.bin just in case something goes wrong or for a future with advanced recovery tools.
Now get the partition table of the disk with:
sudo gpt -r show /dev/disk1
You should get a similar result as this one:
start size index contents
0 1 MBR
1 1 Pri GPT header
2 32 Pri GPT table
34 6
40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
409640 2008
411648 133804032 2 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
134215680 2015
134217695 32 Sec GPT table
134217727 1 Sec GPT header
The first partition is the EFI volume, the second the FAT32 volume of the external disk. Your partition 2 is much larger than the one in the example though.
Even if you get a different output with no GUID partition table but only an MBR
start size index contents
0 1 MBR
1 1
2 134217726 1 MBR part 11
you can continue: encrypting a disk with FileVault requires a GUID partition table - so your disk previously had one. The probability to recover a FAT volume on a disk with a MBR seems to be much lower though. Apparently parts (namely some metadata and volume headers) may be overwritten by FAT32 file system stuff.
The same disk containing an encrypted external HFS+ volume should look like this:
start size index contents
0 1 PMBR
1 1 Pri GPT header
2 32 Pri GPT table
34 6
40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
409640 133545904 2 GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
133955544 262144 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
134217688 7
134217695 32 Sec GPT table
134217727 1 Sec GPT header
The first partition is the EFI partition with a fixed size and start block, the third one is an Apple_Boot partition with a fixed size and start block relative to the last block of the disk and the remaining disk space allocated to the encrypted Core Storage Logical Group. All partitions are aligned to the physical block size of the disk (4096 Bytes).
To restore the old partition table you have to unmount the disk, delete the actual partition table and do some math to create a new one:
diskutil umountDisk /dev/disk1
sudo gpt destroy /dev/disk1
diskutil umountDisk /dev/disk1
sudo gpt create -f /dev/disk1
gpt add -b 40 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk1
Now get the last block number of your disk (in my example that's 134217727) and substract 262183: LastBlockNumber-262183 is the start block of the 3rd partition (Apple_Boot). Add this partition with:
gpt add -b LastBlockNumber-262183 -i 3 -s 262144 -t 426F6F74-0000-11AA-AA11-00306543ECAC disk1
Check the size of the unallocated disk space between partition 1 and partition 3 with:
sudo gpt -r show /dev/disk1
The size of unallocated disk space (UnAlloc) between index 1 and index 3 is probably the size of the old encrypted volume. The size has to be divisible by 8 - please check this! Add this as a partition with:
gpt add -b 409640 -i 2 -s UnAlloc -t 53746F72-6167-11AA-AA11-00306543ECAC disk1 #with UnAlloc= size of unallocated disk space found above
After entering the last command you should be asked for password of the encrypted disk. if not then try:
diskutil cs list
to get a list of CoreStorage items. Try to mount the encrypted volume with:
diskutil cs unlockVolume LVUUID
with LVUUID: the UUID of the encrypted Logical Volume (usually the last one listed). If your main volume is also encrypted choose the proper LVUUID!
If the volume mounts successfully save the most important files and folders to an external volume because mounting the encrypted volume doesn' t necessarily mean that the volume isn't corrupted.
Unmount the volume and run diskutil verifyDisk /dev/disk1 and diskutil repairDisk /dev/disk1. The last command may completely corrupt the disk!
This might still fail. The encrypted volume may still be recoverable though. But then I need more information, because special (invisible) non-file system items have to been read directly from disk with a HexEditor and then restored/replaced.
Best Answer
No. Period.
Nothing is "safely guaranteed." Generally speaking (as at the time of this answer your question is lacking in detail), you can (re)partition without corruption of your data. That's not to say the process is infallible. Problems happen, mistakes can be made. This is why is so important to have a backup of your data.