Time Machine backup to My Book World Edition NAS

How to do Time Machine backups on the My Book World Edition NAS (network attached storage).

  • Set up an additional share at the NAS and mount it on the Mac. Better use an Ethernet wire because it is much faster than the Airport connection. That depends on your router hardware though. Short test showed AFP protocol to be faster than SMB.
  • Create a sparse disk image on the Mac using the Terminal app:
    hdiutil create -size 390g -fs HFS+J -type SPARSEBUNDLE -volname "Backup of " _.sparsebundle
    • 390g: How much space should be used at the NAS for your backup.
    • MAC of en0: The MAC address of the built-in Ethernet device. Get it either by running ifconfig and look for ''ether 00:xx:xx:xx:xx:xx'' in the ''en0'' section or use System Preferences > Network > Built-in Ethernet, click the ''Advanced'' button and the ''Ethernet'' tab. There is the ''Ethernet ID'' which is the MAC actually. Remove the colons from the MAC when using it in the hdiutil command.
    • The name of your Mac as seen in the Sharing system panel at the ''File Sharing'' section. (I don't know how to handle spaces and other special chars - may be you can just escape them by back slash.)
    • Example: hdiutil create -size 390g -fs HFS+J -type SPARSEBUNDLE -volname "Backup of MayasMac" MayasMac_00xxxxxxxxxx.sparsebundle
  • Copy the created disk image to the NAS volume. Delete the file at the Mac - you don't need it there any longer.
  • Allow Time Machine to use the NAS volume. In the Terminal app run:
    defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1
  • Choose the NAS volume in the Time Machine System Preferences panel.
  • Start the Time Machine backup. First time run will take some ours probably.

See also http://forums.macosxhints.com/showthread.php?p=493450 for a discussion about this topic.


Hi, Thanks for the article.

Thanks for the article. When you're creating your 390 GB sparse bundle, does it really work once the disk image is moved to the NAS?
I have a 1 TB My Book World Edition NAS, and I'm trying to configure it to store Time Machine backups of 2 different Macs.
The problem I'm facing is: when I'm using hdiutil locally (on the Mac) to change my sparseBundle's image size, it works, but once moved to the NAS, both the Finder and Time Machine show "978 GB in total", which is the total size of the NAS, not the one I configured for the sparseBundle.
This means that if Mac A has, say, a 200 GB backup and Mac B a 800 GB backup, both future backups will fail because:
- Time Machine thinks it still has lot of room to perform its backup
- technically, the NAS is full
Any idea on how to solve this?