When you use Disk Utility to create a new disk image, it defaults (at least in 10.5) to setting the Volume Format to 'Mac OS Extended (Journaled).' Normally, this isn't an issue, and it's the best setting to use. However, if you're creating a small disk image -- perhaps a 10MB encrypted image to hold your financial records -- it can be a problem. That's because the journaling information takes up about 8MB on the disk image. Add in the space lost when formatting, and you wind up with only 1.7MB of usable space. So if you really need at least 10MB of usable space, create a 20MB disk image instead. Alternatively, you can change the Volume Format to 'Mac OS Extended,' and this will disable journaling on that image. Of the two choices, I've chosen to go with larger images with journaling enabled for those times I need a smaller disk image.

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