I created 50 small (1GB) encrypted DMGs using DiskUtility, and want to combine them into a single 50GB "virtual" drive but still have 50 1G images on disk. How? Why:

  • I want to encrypt my files (even the filenames) before backing them up without using half my disk space just for encrypted files.

  • I use an external backup service that'll backup 1G disk images
    (files), but not 50G files. The smaller the individual disk images, the better.

  • I'm running Mac OS X 10.4.11, so I can't use cryptomfs (plus, I'm not sure if cryptomfs creates several small files or one large file). I have MacFUSE installed, so I tried installing cryptomfs anyway, but it failed (both 1.0 DMG and 1.1 pkg file).

  • Since upgrading is neither free nor easy, I'd prefer to avoid it.

  • I've considered other options (eg, a directory of hard links to the files with encrypted names for the hard links and relying on my backup service for content encryption), but they get fairly complex.


If you are on Leopard (OS X 10.5 or above) you can do this by having one encrypted disk image containing all the files.

The dmg to create in DiskUtility is a sparsebundle. This creates one bundle that mounts as a disk to OSX but actually is a directory and all the files in it are of a much smaller size. In Finder select the sparsesbundle and then Show Package Contents.

I just created a sparsebundle of capacity 1TB and copyied a 400GB vieo file onto it. The structure of the bindle had many files none of which were above 9MB

The band size can be controlled see hdiutil. But I have not done or worked out how do do this.

  • My only options in 10.4.11 are "sparse disk image" and "read/write disk image". As en.wikipedia.org/wiki/Sparse_image#Sparse_bundle notes "Mac OS X v10.5 (Leopard) introduced the concept of the sparse bundle."
    – user2040
    Aug 26 '11 at 22:26
  • Sorry missed that part re the OS - so yes will not work
    – mmmmmm
    Aug 26 '11 at 22:32
  • Can't you upgrade the OS?
    – mmmmmm
    Aug 26 '11 at 22:35
  • I'm guessing that upgrading is neither free nor easy?
    – user2040
    Aug 26 '11 at 22:38
  • 1
    Upgrading is easy but not free but possibly cheaper than the time you spend on sorting out the backups etc
    – mmmmmm
    Aug 26 '11 at 23:31

Unfortunately I don't think there's anything that will do exactly what you're looking for. I think your best option is to symlink them all to a location of your choosing, and make an Automator or shell script that mounts/unmounts them all in one go.

  • I can keep them all mounted at once, but the problem is always figuring out which one is empty enough for what I'm doing. Ick!
    – user2040
    Aug 26 '11 at 22:26

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