Merge Time Machine Backup

Solution 1:

I tried: it works.

Here is how:

I have a time machine volume and a backup of it. I update this backup every two months, using Super Duper.

Recently, several successive mistakes made my time machine volume loose its first two years of backups. I then had a primary time machine volume with all backups but first two years and a backup time machine volume with all backups but latest two months.

I decided to experiment. Starting from scratch on a new hard drive, I copied the backup time machine volume to the new hard drive with Super Duper (backup all files using erase and save option). Then I copied the primary time machine volume on top of that, again with Super Duper (backup all files, using copy files that are different).

I ended with a new working time machine volume including all backups, from day one up to today.

Solution 2:

Simply: Don't!

Time machine uses hardlinks, that you will not be able to recreate by simply copying stuff around. What this means in plain english is you might end up with each copy of the file taking up space - rapidly filling the drive.

Time Machine uses great care to only store each file once - and only takes up more space when the file changes. It assumes everything already stored is correct and won't go back and "fix" any errors you make. It's possible to make a tool to merge the backups, but Snow Leopard makes it easy to browse both backups. Just connect all the drives and option click the Time Machine icon in the menu bar to browse the other backup drives and see that history.

Many people have their time machine data on several drives - you can safely put them on the shelf and move to a new drive rather than go back and edit the past. It's easy to move the whole package to a new drive if needed - just not splice data in to an existing backup folder.

A great place for information is this time machine and internals site and also the Time Machine discussions forum at Apple (I'm assuming we're talking about Snow Leopard here).