Turning off FileVault I'm currently trying to recover my formatted external hard drive with testdisk.
Testdisk takes forever to load on sudo on Mac Terminal, so I tried to approach it from a live Linux Distro, Gparted.
It works so, however it can't write to the Mac HFS+ Drive. At the moment I'm currently trying to partition a separate partition for testdisk to write the recovered files to, however FileVault is in the way.
FileVault is taking forever to finish, (~3 days) and so I followed this  solution and got the following progress.
Logical Volume Family FA9F7FA6-0592-4361-A641-1DAE403816E0
    ----------------------------------------------------------
    Encryption Status:       Unlocked
    Encryption Type:         AES-XTS
    Conversion Status:       Converting
    Conversion Direction:    -none-
    Has Encrypted Extents:   Yes
    Fully Secure:            No
    Passphrase Required:     No
    |
    +-&gt; Logical Volume 21F83719-063D-40EC-8958-36FBD021EE78
        ---------------------------------------------------
        Disk:                  disk1
        Status:                Online
        Size (Total):          998973898752 B (999.0 GB)
        Conversion Progress:   Paused
        Revertible:            Yes (unlock and decryption required)
        LV Name:               Untitled 1
        Volume Name:           Untitled 1
        Content Hint:          Apple_HFS

Seems like it has started to revert, but it is paused and hasn't actually started the process. FileVault on the Settings pane now shows as paused.
How to make revert process continue?
EDIT:I forgot to mention, the Drive Untitled 1 Is my new 1Tb hard drive, which I have swapped out the Mac's original 500Gb drive. It is made by the same company, HGST, and had the same specifications. So there shouldn't be much capability problems.
The last step in the FileVault conversion process is to restart.