It does get bizarre at times though, if/when we try to approach "Backups.backupd" as if it were an ordinary folder... because it's a lot 'hairier' than that.
It is. However, I saw a comment on, I believe, MacOSXHints to the effect that Snow Leopard's Finder will copy "
Backups.backupd" correctly in response to a simple drag and drop. I couldn't find a reference to that anywhere in the release notes, but as it turned out I had a virgin disk drive that I had just gotten with the specific intention of backing up my Time Machine backup. (I had just had my second Time Machine drive die on me, and while I didn't lose any data either time it irks me to lose all that history.)
So I tried it. Finder warned me I might have to authenticate afterwards, but then went ahead and did the copy. I checked the copy every which way I could, and found no problems with it.
du says it was exactly the same number of sectors as the original. All the permissions were correct, including all the ACLs. The extended attributes (including com.apple.metadata:_kTimeMachine{Old,New}estBackup) were copied faithfully.
And when I told Time Machine that I now wanted to back up to the copy instead of the original, it obligingly accepted the copy as a legitimate backup, copying over only the files that had changed in the meantime.
The final test was when I told SuperDuper to copy it again, and SuperDuper (which is certified to clone TM backups correctly) reported the same differences as TM had.
There are situatons however where TM is not quite as efficient as some users might expect. Say we have a huge folder with a zillion items... and we decide to rename (or move) that folder. Instead of recording just that renaming (or moving) "event" somehow... this time, all that recopying (i.e., total duplication of data) does occur. Does it not?
It does. And if you then move the folder back where it was, TM will copy the whole thing again, even though that folder is already present at that location in an earlier backup. TM only compares NOW with "Latest good backup".
I've also noticed that TM does not preserve hard links. If you have two files hard-linked together, TM copies it as two separate files. (You can check this by using (appropriately enough)
ls -li {,/Volumes/*/Backups.backupdb/*/Latest/*}/bin/{ln,link}to verify that /bin/ln and /bin/link are hard-linked to each other, but their TM backups are not.
