Alternaut the comments in the link you posted are causing me some confusion.
There are three reasons for this, for a drive connected directly to your Mac:
- Time Machine will, eventually, fill all the empty space available to it before it begins deleting old backups. When multiple Macs are "competing" for the same backup space, there might be room for several months of backups for one, but only a few weeks for another. This is especially likely to happen if you start backing-up a new Mac to a drive that already has a lot of backups from another Mac. Time Machine on the new Mac will not delete backups from the other Mac(s), so when it needs space for new backups, it will delete the oldest backups from the new Mac instead.
- If you ever want or have to delete all the old backups for one Mac and start over, you can just erase the partition via Disk Utility; if there are other Mac's backups there, they would be erased also. If you replace one of the Macs, Time Machine on the new one won't delete the backups from the old one. And sometimes it's advisable after certain problems.
- You can't copy one Mac's backups to a different, larger drive or network destination; you can only copy the entire set.
- Why would there be any difference if the drive is directly connected to your Mac or on a networked drive such as a Time Capsule? A mounted volume is seen by OS X the same as any other volume whether it is on a local HD, a networked HD, a dmg, a sparse image, or a sparse image bundle. It is just another mounted volume available for access.
- I fail to see any benefit to partitioning in the first scenario. Partitioning will simply cause the larger and presumably older TM data set to overflow first. That may or may not be a desirable outcome. If that statement is intended as an argument for every computer to have its own unique TM drive then I would agree, but the argument is not well made.
- I agree that it is easy to erase a partition and I have never attempted to erase the contents of a sparse image bundle. However I have deleted one of multiple TM sparse image bundles on the same drive and that is just as easy, albeit more time consuming to delete an entire sparse image bundle from a drive (and empty the trash if it is a directly connected drive).
- Why can't you copy one Macs TM backup to another drive at some point in the future? I have done so and it worked perfectly. Granted it can take some time to copy a large sparse image bundle from one disk to another, but it works the same as copying a dmg or sparse image. OS X/Unix treats the sparse image bundle as a single entity and even drag and drop works — or at least it has for me but maybe that is because no one told me it could not be done so I just did it.
Admittedly my experience has primarily been with networked drives either in a Time Capsule or attached to a Time Capsule, but other than making the process slower, I don't see what particular difference that would make.
