I have a client who was using a certain external drive as their Time Machine drive for a while. Then, they misplaced it. So, they got a new external drive and started using that. Now, they've found the original Time Machine drive, and would like to combine the backup from the old drive to the new one.

From the looks of it, the folder for each backup job in Time Machine contains all files from the Mac. Even though it's supposed to be an incremental backup, the "unchanged" files appear in each folder, but they're just hard-links to pre-existing copies on the Time Machine drive (Dirvish, on Linux, behaves this way, too, incidentally).

I have seen suggestions that, to combine the backups, you can just copy the old backup folders to the new drive, but this will waste spaces, as hard-links won't be created when I copy over a file from the old drive which already exists on the new one.

So, it seems that what is needed is a tool which, for each file being copied over to the new drive, will check to see if it's identical to any of the pre-existing versions and, if so, make a hard-link to that pre-existing file instead of creating a new one.

Is there already a tool out there for doing this? Or, is there something else about the process that I'm missing?

  • I'd seriously ask them why they'd want to do this. Do they anticipate needing to go back in time so far to recover a version of a file like that? The new TM drive contains a backup of everything like the old drive, it just doesn't have the ancient history on it. – Ian C. Aug 16 '14 at 20:09
  • I agree with Ian C. in questioning the point of this. You may be able to do so using a third external drive, at the cost of possibly damaging either/both backups. See How Can I Copy My TM Backups to a Different Location – njboot Aug 17 '14 at 4:49
  • 3
    Then you're questioning the point of anybody keeping anything but the most-recent backup of anything. The reason they want this is because they sometimes want to retrieve documents that they deleted some time ago. This client isn't an organized person, I admit. But I also assert that "You shouldn't want to do this" isn't a solution. – Jemenake Aug 17 '14 at 19:02

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