I got a new 2 TB external disk - "yay" - and wanted to use it for both on my Windows desktop and for Time Machine backups. Immediately thought to format it as exFAT but quickly came to realize Time Machine does not support exFAT! Fortunately, there is a workaround...

  1. Plug in your external disk and from Terminal:
  2. Navigate to your removable disk - in my case was called "Removable".
  3. Create a Sparse Bundle of 320 GB using the hdiutil command.
cd /Volumes/Removable
hdiutil create -size 320g -type SPARSEBUNDLE -fs "HFS+J" work-air-backup.sparsebundle

A Sparse Bundle is a disk image comprising a bunch of files. Wikipedia says "Sparse bundle advantages for Time Machine: the backup destination no longer needs to be a HFS volume" - which is exactly what I needed!

  1. Then open finder to and double click the on the .sparsebundle file to mount it.
  2. You should rename the "untitled" disk on the desktop to something more sensible, e.g. "work-backup".

Finder .sparsebundle disk image

  1. Next, you need to set permissions on the files within the sparse bundle disk image. To do that, you'll need to get the ID of the disk, so back in Terminal:
    diskutil list

In my case disk1 was my internal SSD (not shown below), disk2 (external, physical) was the external disk, and disk3 (disk image) was the mounted sparse bundle. Make a note of the IDENTIFIER that matches the NAME you gave your previously "untilted" sparsebundle in step #5 above, in my case disk3s2.

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *2.0 TB     disk2
   1:               Windows_NTFS                         2.0 TB     disk2s1

/dev/disk3 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +322.1 GB   disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS work-backup             321.8 GB   disk3s2
  1. Enter the diskutil command as below (entering your password if prompted), replacing disk3s2 with your identifier if its not the same as mine!
  2. Then enter the next tmutil command, to set the mounted sparse bundle as the Time Machine destination volume.
sudo diskutil enableOwnership /dev/disk3s2
sudo tmutil setdestination '/Volumes/work-backup'
  1. Now, open the Time Machine preference pane in System Preferences, and turn Time Machine on. That's it - you've set up Time Machine with exFAT!

When the backup is done, as usual Eject (unmount) the sparse bundle, then Eject the removable disk as usual.

Next time, to backup, simply:

  1. Plug in the removable disk and open it in Finder
  2. Double click the sparse bundle to mount it.
  3. Open up System Preferences > Time Machine and start the backup.

Easy! FYI my source for info was a Macworld article dated April 2014.

Long time no post. Hope this helped you!

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