How do I backup the *contents* of a sparseimage (but not the actual image)?

Question

This is related to my iPhoto question:
http://discussions.apple.com/thread.jspa?threadID=2590319
I'd like to backup the contents of a sparseimage using TM. If I just point TM to the imagefile, I run in to the issue that each time I add/modify a file inside the image, then TM marks the whole image as changed and hence backs it all up. And since the image is large I run out of diskspace.
Is there some way I can just back up the contents of the image? If my sparse image file is:
/Users/shared/foo.sparseimage and it gets mounted as:
/Volumes/foo
is there someway I can point TM to /Volumes/foo and then exclude TM backing up /Users/shared/foo.sparseimage (I know how to do the latter).
Thanks in advance.

Answer 1

each time I add/modify a file inside the image, then TM marks the whole image as
changed and hence backs it all up. And since the image is large I run out of
diskspace.
If you use a sparsebundle disk image instead of a sparseimage, that shouldn't happen.
From this article
[Discovering Sparse Bundle Disk Images|http://db.tidbits.com/article/9673]:
A sparse bundle looks and acts just like a sparse image - it can grow in size, can optionally be compressed or encrypted, and so on. What's different is that it isn't actually a single file, as all previous disk image formats were. It's a bundle (also known as a package) - a folder that Mac OS X treats as a single file, which is also true of applications. (To verify this, you can Control-click or right-click a sparse bundle, choose Show Package Contents from the pop-up menu, and browse through its contents.) Inside that package is a folder full of bands - files that are each 8 MB in size, as many as are needed to hold the image's data.
What's cool about this is that if you change something on a sparse bundle (adding or modifying a file, for instance), only the band(s) containing that data change, not the whole bundle. As a result, assuming your backup software treats the contents of bundles as individual files, you no longer have to back up a huge disk image just because a tiny file changed. Your backup software only has to copy the 8 MB band(s) containing any of that file's data (often only one). So I converted my encrypted sparse image to an encrypted sparse bundle, and now I can include it along with all my other files in my ordinary backups.
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