The upgrade to Snow Leopard breaks 10.5.x Time Machine backups configured with AFP shares on network volumes, as per this older hint, for example.
After some trial and error, I was able to find out that the secrect lies with a hidden property list file that specifies the hardware UUID for the machine to be backed up. The following are some simple instructions to set up a new backup volume from scratch. They may work for upgrading a Leopard Time Machine disk to Snow Leopard, but I have not been able to verify this.
Setup: If your Time Machine is already configured to back up to a networked AFP share, move on to the next step. Otherwise, follow the setup procedure in the above-linked hint.
Simple method: Use the script and directions that I posted on the InsanelyMac forums.
Manual method:
- Create a disk image named the same as your machine's computer name (not sure that this is crucial; you can find it in System Preferences » Sharing). This example is for a 500GB (max size) image for a machine named snowy:
hdiutil create -size 500G -fs HFS+J -volname 'Time Machine Backups' -type SPARSEBUNDLE snowy.sparsebundle
- Create a new text file, and copy and paste the below code. inserting your machine's hardware UUID in the noted spot -- you can find your hardware UUID in System Profiler. Save the file on your Desktop as com.apple.TimeMachine.MachineID.plist.
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>com.apple.backupd.HostUUID</key> <string>YOURUUIDHERE</string> </dict> </plist> - Copy the modified com.apple.TimeMachine.MachineID.plist file into your disk image directory: cp ~/Desktop/com.apple.TimeMachine.MachineID.plist snowy.sparsebundle/
- Copy your disk image file to your mounted backup volume. This example assumes an AFP share with the name backups: cp -pfr snowy.sparsebundle /Volumes/backups/snowy.sparsebundle
[robg adds: I haven't tested this one.]

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