Migrate Time Machine to a New Folder Structure

[haravikk]

Okay, so I currently have a full Time Machine backup of roughly 3tb, however, I'm currently planning a clean install on my machine and will be changing my file structure; for example, currently I have two separate volumes (Mac OS & Users, Files) that I will be combining into a single volume.

What I'm wondering is how Time Machine will cope with this? I'll likely restore from backup manually, as I'll never be able to leave my machine on long enough to copy everything in a single day, but I want to make sure that when I do copy everything that I can start backing up again where I left off, without having to do a full backup.


I'm not sure however what support Time Machine has for this, for example, can I use the Terminal to change hard-link targets so that my backup (roughly) mirrors the new structure, for example, I would move the contents of the Files volume backup into the same folder as my Mac OS & Users backup, then rename to match the new volume, all within the latest backup. If this is possible then how do I go about doing it, and is there anything I will need to avoid doing? I know Time Machine somehow applies strange permissions to a backup volume that prevent most tampering. Are there any tools for doing anything like this automatically; e.g - to just scan my machine and move my backup around until it matches?

 

[Bear]

Don't muck with the file structure in the Time Machine backups. I hear stories of people who have tried manually playing with the backups and breaking their backups totally. And this was for things that you could do with Time Machine with the available options and not break things.

Your best option is to buy another external disk and start a fresh Time Machine disk. And hold on to your current TM disk as is until you no longer need the backups on it. I'm seeing 3 TB USB 3 external drives for about $120 US.

 

[haravikk]

Don't muck with the file structure in the Time Machine backups. I hear stories of people who have tried manually playing with the backups and breaking their backups totally. And this was for things that you could do with Time Machine with the available options and not break things.

Your best option is to buy another external disk and start a fresh Time Machine disk. And hold on to your current TM disk as is until you no longer need the backups on it. I'm seeing 3 TB USB 3 external drives for about $120 US.

I have a NAS as well which has almost finished a full-backup; I decided I wanted the second lot of redundancy before I did a clean install.

But since I'll have two full backups once I've restored my machine, then it doesn't seem like there's much risk in fooling with the Time Machine structure of one of them since Time Machine will only wipe it to make room anyway if I leave it as-is, might as well try to sync up the folder structure if it means I only need to backup a few gigabytes rather than the full 3 terabytes

 

[haravikk]

Okay so I had to return to this again but I was able to find a solution for anyone interested.

It's quite technical, so definitely don't do this if you're not comfortable using the Terminal. The command you'll want to investigate is hidden under:

/System/Library/Extensions/TMSafetyNet.kext/Helpers/bypass

It's a lot like running sudo in that it takes as arguments another command to run. You'll also likely need sudo, so I recommend running "sudo su" to run all commands as root as it eliminates a few extra headaches.

For example, you might do the following:

sudo su
bypass='/System/Library/Extensions/TMSafetyNet.kext/Helpers/bypass'
$bypass mv foo/bar bar/foo

Or rm or whatever command you need. Unfortunately the mechanism isn't completely reliable, as mv will sometimes fail regardless for no reason that I can fathom. For this reason I recommend installing the coreutils package via Macports in order to get the gcp command. This is a version of cp that supports creation of hard-links, so if your move fails you can do something like the following:

$bypass /opt/local/bin/gcp -lR foo/bar bar/foo

All of this is very much experimental and shouldn't be attempted on your only backup. However if you, like me, have a backup but have changed the structure of your setup, either by renaming a folder with a lot of data inside, done a clean-installation with a new volume layout etc. then it's worth attempting this so that Time Machine can continue where it left off (to a degree). Otherwise Time Machine will just destroy your backups anyway to make room creating new copies of everything.

 

[shafeeqts]

Stop Time Machine from offering you to use all new disks

"defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool true" use this terminal commands for Stop Time Machine from offering you to use all new disks: source and more OS X Mountain Lion terminal commands.