Combining multiple small DMGs into one large “virtual” DMG

Question

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.

Answer 1

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.

Answer 2

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.