The issue that makes Time Machine more difficult in terms of options for backup locations is that it requires use of Apple’s proprietary HFS+ filesystem. Although I’m certain the HFS+ features that Time Machine uses for file versioning and linking could be “mimicked” for use on other more open filesystems, the reality is that Apple chose HFS+ and supports that filesystem exclusively in Time Machine (in fact as of this writing Apple’s new APFS isn’t even supported for Time Machine backups as of yet).
- Create a Windows share location
- Make the remote share automatically mount
- make Time Machine use the remote share and file
- Check Time Machine
Create a Windows share location
I won’t go into detail on how to create a shared folder on a Windows PC but before you begin, you’ll need to have a share created and accessible to your Mac that you want to run Time Machine on. For example, if you have a Windows PC named “Server” and a network shared folder on the Windows PC named “share”, you’d be able to test for connectivity by doing the following:
- Start Finder.
- Click GO > Connect to Server.
- Enter smb://Server/Share where “server” is the name of the Windows PC and “share” is the name of the shared folder.
- Click Connect.
If you’ve properly set everything up, you’ll be prompted to enter a registered user and password. Make certain to save those credentials to your keychain for the OS to automatically use those credentials for connecting to the share for future access. You should also see that share in Finder in your “Shared” section and see the “Eject” icon next to it since it is now mounted.
Create a sparsebundle image
We now need to create an “image” file that will, in essence, pretend to be an HFS+ filesystem for your Mac to back up to.
- Start Disk Utility.
- Go to File > New Image > Blank Image.
- Rename the Save As to TimeMachine.
- Press the Down Arrow next to Save As.
- Select your mounted Share.
- Rename the Name of your sparsebundle.
- Select the Size of the backup location. Be generous. If you want to be able to at the very least backup the entire contents of a full hard drive, elect a size at least equal to your Macintosh HD drive size. As a word of warning, the size you choose will be the size of the disk space that will be immediately created on the remote share.
- Make certain that the Format is set to Mac OS Extended (Journaled).
- Click Save. This will take a while especially if you set a large file size.
- Click Done.
Make the remote share automatically mount
In order for this hack to survive reboots, we need to ensure that the remote share is automatically mounted when you restart your Mac. Here is a simple way to get this done. Some drawbacks of this method are that it only works once you’ve logged in and it won’t work for other users of your Mac.
- Start System Preferences.
- Select Users & Groups.
- Select your Username.
- Click Login Items.
- Click the +.
- Navigate to and select your mounted share and TimeMachine.dmgfile we created earlier.
- Click Add.
You may need to unmount the share before this can take effect but as of this moment, that share will automatically mount every time you reboot and log in.
Make Time Machine use the remote share and file
Finally, we’re ready to make Time Machine see and use the Windows 10 share housing our sparsebundle file.
- Start Terminal.
- Enter the command sudo tmutil setdestination /Volumes/TimeMachine/ where “TimeMachine” is the name you gave to your sparsebundle you created with Disk Utility.
- Enter your Password.
Check Time Machine
Now we just need to check that Time Machine sees the disk and is ready to use it for backups.
- Start System Preferences.
- Select Time Machine.
- You should now see that Time Machine has a backup location and Select Disk shows the proper name of the sparsebundle.