Okay - so I have a relatively simple question but can't find a clear answer.

Say for instance I have a large video file in FolderA named something.avi. Time Machine then makes a pass and backs this up. Afterwards, I rename this file somethingelse.avi.

Does Time Machine physically copy all of this data a second time, or does it create a new link with the changed file name, which points to the data which has already been copied?


Anytime you make a change to a file Time Machine makes a new copy of the file:

John Siracusa's Mac OS X 10.5 Leopard: the Ars Technica review/Time Machine:

It's unfortunate that Time Machine's cleverness does not extend just a bit further. The smallest unit of data that Time Machine will backup is an individual file. That means that if you change one byte in a 10GB file, that entire 10GB file needs to be copied to the backup volume. Hard link can't help you here. There's no way to make a hard link to "9.99999GB of the old data, plus this one byte of new data."

The beauty of Time Machine is that it automatically deletes the older copies of files from the backup when it needs to recover the space.

  • Thanks, now that you posted clip, I'm pretty sure I read that exact post a couple of years ago. – delvec Feb 16 '12 at 6:02
  • The above answer does not answer the question. The question is not "what happens if I change a file, even just a little bit", the question is "what happens if I rename a file" which does not change the file at all. – user71929 Mar 3 '14 at 2:32
  • @Daniel Time Machine makes a new copy if you rename a file. I think the make a change includes rename, but wanted to answer your comment directly. – bmike Mar 3 '14 at 3:19

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