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>.sparsebundlein the Finder each time you plug the drive in. After that, Time Machine backups will run as normal.
- 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
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.
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.plistfile 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 (
- 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.
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.