Time Machine Size Limits

So I have this new My Book World Edition, and I set it up to allow for Time Machine backups. The problem? On OS X, Time Machine wants to eat up almost the entire amount of free space before it goes about deleting old files… (un)conveniently there is no option to restrict the size of the backups.

Never fear… I google’d a bunch and found that if you run the following command on the Mac doing the backups:

defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 209715200

It doesn’t appear to do anything (or may possibly do something else that isn’t related to what I was after). 🙂

So, I went about it in a different manner. If I clicked on the Time Machine icon (rotating clock) in the menu bar, and clicked “Enter Time Machine”… exited the GUI of Time Machine, and then opened terminal, I could do the following:

  1. Become root:
    sudo -s
  2. Goto the /Volumes directory, and look for which folder is mounted for Time Machine backups:
    cd /Volumes && ls -l
  3. Enter the folder that is mounted for Time Machine backups:
    cd $Mount_Point_For_Backups
  4. Look for the .sparsebundle file that is being used for backing up the workstation:
    ls -l
  5. Resize the sparsebundle file:
    hdiutil resize -size 200g $hostname.sparsebundle

The sparse image is then resized, and Time Machine will report that there is only around 200 gigabytes total available space rather than around a terabyte (which is the original size of the drive). 🙂


  1. Thanks for the info, one small point, after using the time machine GUI the bundle will be mounted and you will get a temporarly unavailable error.

    You need to go into Disk Utility, right click on $hostname.sparsebundle and unmount/eject it before resizing.

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