External Drives and Time Machine
Chris Hands Thankfully the solution is fairly straightforward. The following is lifted directly from Apple knowledge base article #306932:
Important: Erasing a disk deletes all files on it. Make sure that you have or make a copy of important files in another location first.
Open Disk Utility.
Click the Partitions tab.
From the Volume Scheme pop-up menu, choose the desired number of partitions.
Click the Options button.
Select a new partition scheme:
Use "Apple Partition Map" partition scheme if the disk will be used with Time Machine and a PowerPC-based Mac.
Use "GUID" partition scheme if the disk will be used with Time Machine and a Intel-based Mac.
Click OK.
Click Apply.
Once the external hard disk is repartitioned, select it again in Time Machine preferences and use it for your backups.
Elsewhere I've found an article that advocates making two partitions and then reverting to one (from Gizmodo):
• Go to the Partition tab. Create two partitions. Under Options, select GUID Partition Table (what you would use to make a Mac OS boot disk) and click OK then Apply.
• Once your partitions are in place, do it again, reverting back to just one partition, but still keeping the GUID Partition Table option. Click OK and Apply again, and at this point you should be cool.
• To be safe, you can then go to Erase and set formatting for Mac OS Extended (Journaled), then format it once and for all. But when you get there, you will probably see that your volume is already formatted in the right way.
UPDATE: Some people have gotten this to work without creating two partitions. If you like, try creating just a single partition, but using the GUID Partition Table option. This may be all it takes to break the chokehold.
Hope those of you who're interested in this find this useful.
Btw, for those that are interested, GUID stands for Globally Unique Identifier, and the advantages it has over the Apple Partition Scheme can be found at
http://lists.apple.com/archives/Macos-x-server/2006/Apr/msg01335.html.
By the looks of it, GUID is actually superior as a Time Machine HD format on either platform as the only disadvantage it really has is an inability for PPC macs to boot from it - however Time Machine backups are not bootable anyway.