First of all, fie on Apple for giving both their cloud storage service and their backup program names that are almost completely google-proof. They’ve recently corrected one of those by renaming “dot mac” to “MobileMe” but calling your backup program “Backup” is a great way to make it really hard to investigate. It’s like, imagine how hard it would be to do a background check on someone named John Doe.

So I use the Dot Mac Backup and it works pretty smoothly, which is the second most important feature in a backup program. (The most important feature is the ability to actually restore files.) But then one day it said that to incrementally back up my “Home Minus Media” set — the set containing my Home Folder, but excluding big-ticket items like Music, Movies, Backups, Downloads, and so on — would require 63 DVDs. WTF?

It turned out that the problem occurred after I trashed a few old DVD rips that I had finished watching, and the culprit was the directory /Users/chaffee/.Trash. Seems like the UI was helpfully excluding it from the list of subdirectories of /Users/chaffee, it being a system file and all, so I couldn’t mark it to exclude. That’s OK, I think, I’m a power user, so I’ll just check the box that says “Show invisible system files.”

Except there’s no such box. Try as I might, I can’t find a way to exclude the Trash folder from the UI. I had to dig into the file system and edit Backup’s own data file, as follows.

• In Backup, create a backup set and exclude at least one item in it
• Quit the Backup app
• In Finder, open up ~/Library/Application Support/Backup/BackupSets
• There will be a list of randomly named .backupset folders. Each contains a folder named Contents. For each, use Quick Look (hit Space) on and a file named InfoPlist.strings to find the one containing your set.

• Open its sibling named User.quickpick in a text editor like TextMate.
• The “quickpick” file is actually a folder, so open up the file buried under there named DefinitionPlist.strings
• Find the section “Prune Paths” and add an entry for ~/.Trash

• Save the file and relaunch Backup.

You should see the “.Trash” entry excluded as if you had clicked on it — which you would have if they had showed you the silly thing in the first place.

As you can see from the screenshot, I’ve still got some excess gigabytes to hunt down and exclude, but at least I won’t get burned the next time I erase a metric buttload of pr0n– uh, I mean, content I legally acquired and temporarily transferred onto my personal computer in compliance with the DMCA.