A rookie question about .dmgs...

[RAMd®d]

Speaking in round numbers, if I have an empty 5G dmg, an want to put 5G of data on it, I'll need 10G of free space, correct?

It's been a long time since I did this, and I don't remember any details.

[macphanatic]

IIRC, no. I set up a password protected dmg file years ago. As I added files, I don't think that the dmg file size increased.

[m.paris]

If you have an empty 5G dmg you can put 4G+ in and the size will remain 5G. Putting in 5G will be a tight squeeze. When the dmg is created it has a fixed size just like a regular disk. But if it is created as a sparse image, a maximum size can be set and you can fill it up to that amount. If the original (sparse)dmg is set for a 100G maximum you are okay but if the original was set for 5G max, then you need to create a new one (either a dmg or a sparse image). I don't recall what the default size for a new sparse dmg is (26 MB?). It grows automatically to accommodate whatever you put in up to the maximum. To paraphrase a Missing Manual segment: a dmg is like a steel bucket and a sparse image is like an accordion file.

[Article Accelerator]

Rammie, this will save you lots of time and trouble:

OS X provides the tools to "roll your own" solution in less than a minute using Automator:
- launch Automator and create a new Service workflow
- set the workflow to receive selected Files or Folders in Finder.app
- drag-and-drop the New Disk Image action (in the Files & Folders library) into the workflow and set the action's options according to your requirements
- save the workflow
From now on, you'll be able to instantly create an encrypted disk image from files and folders or any combination thereof via the Finder's contextual menu.

[RAMd®d]

Guys, thanks for the info.

AA, that's the ticket!

Thanks!