Use a Windows NTFS, or Linux, or other–formatted disk for Apple Time Machine Backups

It is well known that you have to use an Apple formatted disk (HFS+) for Time Machine Backups and you can’t use an NTFS formatted disk, or any of the preferred *nix disk formats with Time Machine.

Except you can.

Gotchas And Caveats

It’s not always a first choice option:

  • If your Windows drive is connected over USB2, it will be much slower than a Mac disk connected over Thunderbolt or FireWire. My first backup of 120GB took about 10 hours, aka all night. But that was still better than no backup whilst waiting for a new drive to arrive in the post.
  • The backup volume will not auto-mount when you plug the drive in. You must manually double-click the <YourMachineName>.sparsebundle in the Finder each time you plug the drive in. After that, Time Machine backups will run as normal.

Instructions

  • Plug in your foreign-formatted disk and get a read/write driver for it
  • Save the the script from tmMakeImage script in, for instance, your Downloads directory.
  • Open a terminal window.
  • If you saved to Downloads, then something like this should make the script executable and show you command line usage:
    cd ~/Downloads
    chmod a+x tmMakeImage
    mv tmMakeImage /usr/local/bin
    tmMakeImage
  • So if your external drive has a Volume called WinDrive, and your Mac drive is about 250GB then this command should initialise it for Time Machine backups:
    tmMakeImage 500GB /Volumes/WinDrive GO
  • Optionally, follow up with an immediate tmutil startbackup

Opening the Time Machine preferences should now show that you have “Time Machine Backups” selected as your backup drive. Don’t forget to double-click the sparsebundle each time you attach the drive, to mount your Backup Volume and allow Time Machine to do its stuff.

Background

Using Sparsebundles to create HFS+ formatted drive on a ‘foreign’ disk format

Apple created, it seems, sparse images and sparse bundles to solve the problem of saving backups on a network drive. Time Machine uses and recognises them. It will even auto-mount the sparsebundle disk image when you re-attach the drive in order to start running a backup.

Local drives and network drives

Most instructions on the web focus on network drives. Good instructions without any command-line stuff is here: http://www.hciguy.com/2010/06/16/using-time-machine-to-backup-your-mac-to-an-ntfs-drive-over-the-network-running-win-7/ For network drives, the sparsebundle name includes your Mac’s MAC address which it doesn’t need to for a locally-connected drive.

Things Under the Hood of Time Machine Disks

  • You can’t create a sparsebundle directly on a network or ‘foreign’ drive so the typical thing is to create it on your machine first, and then copy it to its final destination.
  • Sparsebundles don’t use up empty space. An sparsebundle declared as 500GB but still empty will only take up a few megabytes of real disk space.
  • A sparsebundle used by Time Machine has a com.apple.TimeMachine.MachineID.plist file in the package, which contains the UUID of the physical machine it belongs to. This stops you accidentally using backups on the ‘wrong’ machine. (Time Machine does let you browse and use ‘wrong’ backups though).
  • A Time Machine drive must have “Ignore ownership permissions” Off, whereas by default the Mac mounts external drives with “Ignore ownership permissions” set to On. This setting is not stored on the drive itself; it’s stored on your machine and can be specified each time the drive is mounted (man hdiutil) or specified permanently (man vsdbutil)
  • You can set the Time Machine destination to a sparsebundle on an attached drive by first mounting it then doing tmutil setdestination /Volumes/Volumenameonceitsbeenmounted. You mount the image either by double-clicking it in Finder, or with hdiutil attach /path/to/image.
  • Learn More:
    man tmutil
    man hdiutil
    man vsdbutil
    
  • You can still use your backup disks for other files alongside your Time Machine backups. Just don’t touch the Backups.backupdb folder! The Finder will protect it to some extent; it doesn’t let you modify things in there, but it will let you delete and add things.
  • The Script

    Most of the things in the tmMakeImage script can be found on the net going back to 2007, but you’ll still find recent answers on the internet saying it can’t be done.

5 thoughts on “Use a Windows NTFS, or Linux, or other–formatted disk for Apple Time Machine Backups

  1. Krish

    I followed the instructions above. I created sparse bundle file. But when I click on the sparsebundle file, Time Machine Backups appears in finder for 0.5 minute and then disappears and I am do not see the disk in Time Machine either. I did install Fuse OX NTFS-3G. Did I miss something? My Mac version is 10.6.8.

    Reply
    1. Chris F Carroll Post author

      Hi Krish,
      Interesting. It could be quite hard to track down why the sparsebundle image unmounts like that. My first guess is that it’s to do with your OS X version and that 10.6 doesn’t want the com.apple.TimeMachine.MachineID.plist file inside the sparsebundle like later versions do.
      So, try:
      1) Manual create the sparsebundle image in Disk Utility
      2) Double click it.
      3) If it stays mounted, then open Time Machine and see if appears in your list of disks to save to.
      OR:
      Try the instructions in http://code.stephenmorley.org/articles/time-machine-on-a-network-drive/ from about step 4 (ignoring the network drive stuff) and see if that works better?
      Those are my first ideas, anyway.

      Reply
  2. Krish

    Hi Chris, Thanks for the suggestion. I tried following the instructions on the website you cited. The end result is still the same. The sparsebundle created using those steps mounts and stays mounted for few seconds and then disappears. It does not show up on Time Machine during that short duration either.

    One thing I did not share with you is that I had to install NTFS-3G to make my NTFS hard drive writable. Do you think it has to do with this “custom” Sharing and Permisssions I have on this drive?

    Many Thanks,
    Krish

    Reply
    1. Chris F Carroll Post author

      The Apple Forums post suggests that it’s a problem for specific OS X versions so upgrading a version or so might help. I guess that so long as you have at least read & write permissions on the drive, the ‘custom’ settings don’t matter much. Sorry I haven’t got anything more helpful.

      Reply

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