Configure Time Machine to Save Backups to a TrueCrypt Volume

Recently I created a TrueCrypt volume on my Drobo array to contain my Time Machine backups on my iMac.  The key benefits that made me go this route:

1) Disk space is pre-formatted and gives me faster write times than writing directly to the Drobo file system.
2) Time Machine max size is limited by the size of the container (easier to manage than command line overrides which can cause headaches as the OS is updated in the future).
3) Many more encryption options than Time Machine gives.

I formatted the TrueCrypt volume to be Mac OS Extended (Journaled), however when completed the Time Machine GUI was unable to select it as a backup disk even when it was mounted.

The solution?  To the command line! Type the mount command and determine the name of the drive that you want to backup to. You should see something like this.

Davids-iMac:~ david$ mount
/dev/disk0s2 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk1s2 on /Volumes/Drobot (hfs, local, nodev, nosuid, journaled)
TrueCrypt@osxfuse0 on /private/var/folders/3s/zqga25x17gldc_5chs7qt1ch0000gm/T/.truecrypt_aux_mnt1 (osxfusefs, nodev, nosuid, synchronous, nobrowse, mounted by david)
/dev/disk2 on /Volumes/TimeMachine Drobot (hfs, local, nodev, nosuid, journaled, noowners, mounted by david)

The name of the drive I want is TimeMachine Drobot.  So, I’m going to use this information to add this drive as a TimeMachine destination:

Davids-iMac:~ david$ sudo tmutil setdestination /Volumes/TimeMachine\ Drobot/

Replace /Volumes/TimeMachine\ Drobot/ with the location of your drive.

Double check to see if the destination is correct:

Davids-iMac:~ david$ tmutil destinationinfo
====================================================
Name          : TimeMachine Drobot
Kind          : Local
Mount Point   : /Volumes/TimeMachine Drobot
ID            : 12345678-1234-ABCD-ABCD-1234ABCD1234

If it’s not, you can remove the destination with the tmutil removedestination command.  But assuming everything went correctly you should now see the drive is set up as a backup drive in the Time Machine Preferences GUI.  Simply turn on Time Machine backups, and you should be good to go.