In Snow Leopard it's rather easy to have multiple Time Machine backups with different settings. You can simply write a script to change the preference files for the two (or more) different drives.
Up until now, my Time Machine has always been backing up on different drives without even turning it off or on again to let it accept the new preferences.
You can let your script run automatically with Do Something When, or some other third party location managers, or even as a repeating alarm in iCal, so you'll never have to worry about Time Machine again. Or you can simply run it manually of course.
This script can be used as a template. The following list of variables is used, and you will substitute the names you actually use for your disks and filenames:
- property pth: Path to Preferences folder, change the Volume name if necessary.
- property d1name: Name of the first backup disk.
- property d1: Time Machine prefs named after first backup disk.
- property d2name: Name of the second backup disk.
- property d2: Time Machine prefs named after second backup disk.
- property active: The current active Time Machine prefs file.
property pth : "Macintosh HD:Library:Preferences:" property d1name : "Full Time Machine" property d1 : "com.apple.TimeMachine Full.plist" property d2name : "Tiny Time Machine" property d2 : "com.apple.TimeMachine Tiny.plist" property active : "com.apple.TimeMachine.plist" do shell script "defaults write com.apple.TimeMachine AutoBackup -bool false" if (list disks) contains d1name then tell application "Finder" to if exists (pth & d1) then set name of file (pth & active) to d2 set name of file (pth & d1) to active end if else if (list disks) contains d2name then tell application "Finder" to if exists (pth & d2) then set name of file (pth & active) to d1 set name of file (pth & d2) to active end if end if do shell script "defaults write com.apple.TimeMachine AutoBackup -bool true"
[crarko adds: I haven't tested this one, but did fill in my variables and compile the script. There's a previous hint that discussed doing this manually.]

