How to Migrate Time Machine Backups to a Larger Disk

One day it's bound to happen: Your Time Machine Backup Disk is full and there are too many changes for Time Machine to make a new backup. Or you simply think you'd feel more comfortable having more older files. So you go out and buy that coveted 3TB FireWire drive that you always thought you'd want for your backups. But how to proceed?

Well, first of all, turn off Time Machine in System Preferences for a moment, so the OS doesn't try to back up anything while you've got your fingers in between the moving parts of the hard disk. Yeah, I know, uncomfortable feeling.

First, initialize (or "format") the new backup drive using Disk Utility's "Partition" pane, if you haven't done so already. Chances are it came from the factory formatted as FAT or NTFS or some other Windows file format, while Mac OS X prefers "HFS+ (Journaled)". Make sure you choose "GUID Partition Table" from the choices the "Options" button gives you.

If you have a traditional Time Machine setup, where the drive is attached directly to your Mac, you'll need to use a tool like SuperDuper! or Apple's very own Disk Utility to create a one-to-one copy of all the files on there. Since Time machine uses special symbolic links on its drive, and also uses a bunch of invisible files, just copying over the files you see won't work.

If you've selected a networked drive attached to another Mac in Time Machine, Time Machine will have created a disk image on your old backup disk, plus a bunch of invisible files. The disk image wraps all the complicated symlinks, so part of the difficult stuff has already been made easier. Just copy over the disk image and all the invisible files.

The latter can be done using Terminal. Just type in the command and parameters, then drag in the file/folder you want to copy, and the disk you want to copy to. So if your old drive was called "My Backup Disk" and your new one was called "My New Backup Disk", you'd use cd /Volumes/My\ Backup\ Disk to tell it you want to look at your backup disk, and then ls -al to see all files and folders where the latter are indicated by a "d" at the start of the line. Then do a cp .com.apple.timemachine.supported /Volumes/My\ New\ Backup\ Disk/ for files (in this case the file name is ".com.apple.timemachine.supported"), and cp -R .fseventsd /Volumes/My\ New\ Backup\ Disk/ for folders (in this case the folder in question is called ".fseventsd"), adding the word sudo at the start if you get permission errors.

Alternatively, many file browser tools exist that allow showing and copying invisible files. You don't need the .DS_Store, .Trashes, .Spotlight-V100, Desktop DB or Desktop DF, nor any .VolumeIcon.icns file you may have, but I copied everything else. Of course you can also just use SuperDuper! for this, or Disk Utility.

Once you have that copy, simply rename your old drive, and give its name to the new drive. You might have to unmount both drives and re-mount them, but then Time Machine should automagically use the new one. After all, it has the right name and contains all the right data.

Alternatively, you can just select the new drive as a new destination in Time Machine, I guess.

Turn back on Time Machine and start a backup. That's it. Be sure not to delete the old backup until you're abolutely sure it worked: Enter Time Machine and rewind a bit. Old files still there? New files there? Good. Now, if you don't need the disk space on the old backup, leave it there for a while. You'll never know, and a little redundancy is always good.

Pretty easy, isn't it?

Reader Comments: (RSS Feed)

wtr writes: Hey, great description! Have to read this in more quietness than possible here in office. But looks very promising! Cheers, wtr

Or E-Mail Uli privately.