10.5: Create a Time Machine size limit for networked disks

Nov 21, '07 07:30:03AM

Contributed by: Anonymous

I am using Time Machine to back up my MacBook Pro on a Samba drive connected to a Linux machine, per this hint. The thing is that when you use Time Machine, it will fill up your disk with backups. However, since I am using a shared networked drive, I wanted to leave free disk space for other users and keep my sysadmin happy. So, here is how you can prevent Time Machine from filling up your networked disk.

First, when you use Time Machine with a SMB disk, it creates a .sparsebundle disk image to put the backup data into. The disk image has a capacity of 2.75 TB. Since my SMB disk has only 1.5 TB of capacity, the disk image shows that 1.25TB is used and 1.5TB is available. The trick is to create another sparsebundle disk image of a given capacity (I used 300GB) on the SMB disk. Use 'Mac OS Extended (Case-sensitive, Journaled)' as the volume format in Disk Utility. Name the volume the same as the volume used by Time Machine (it should be Backup of computerName), and save it to something like test.sparsebundle.

Then, turn off Time Machine, mount your Time Machine backup image (by opening the .sparsebundle disk image on your SMB disk) and your newly-created disk image and use Disk Utility to 'restore' the Time Machine disk image into your new image. Click on the 'Erase Destination' button in order to allow Disk Utility to make a block copy of your Time Machine disk image. Wait for the process to finish.

Once finished, unmount both images and open a Finder window into your SMB drive. Note the name of the disk image used by Time Machine; it should be computerName_ABC123DEF.sparsebundle, where ABC123DEF is your MAC address. Delete this image, and rename your test.sparsebundle to this name. Then, restart Time Machine. The next time it backs up, you will see that the backup disk image used by Time Machine now has a new capacity (300GB in my case), and Time Machine will not fill up your network disk. It will use no more than 300GB.

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