Since hard drives have a limited lifespan, it's important to change the Time Machine backup drive every few years, or when it begins to show signs of wear. When switching Time Machine drives, it's important to transfer the files to the new drive properly to avoid damage to backups.
In this tutorial, I’ll show you how to prepare a new external hard drive for use with Time Machine and how to move existing backups to the new drive.
Preparing a New Drive for Time Machine
Note: This process will erase all data from the external hard drive. If you have any important data on the drive, ensure you back it up beforehand.
Before transferring your backups, you need to prepare the new drive for use as a Time Machine compatible backup drive by formatting it for use as an OS X compatible drive.
Start by plugging the new drive into the Mac and launching Disk Utility from the Applications folder or by searching for the application in Spotlight. Look towards the left-hand side of the Disk Utility window and click on the new external drive's name.
Look towards the center of the window and click into the Erase tab. Ensure Mac OS Extended (Journaled) is selected from the Format drop-down menu, give the drive a name, and click the Erase button from the lower right-hand corner of the Disk Utility window.
The drive will be erased and is ready for use as a Time Machine drive.
Disabling Time Machine on the Existing Backup Drive
Time Machine must be disabled on the current backup drive. Doing this is simple: look towards the right-hand side of the Apple toolbar and click on the Time Machine button.
From the drop-down menu, click on Open Time Machine Preferences.
Look towards the center of the right-hand side of the window and slide the large OFF/ON slider to the OFF position. Time Machine backups will no longer take place on this drive.
Moving Time Machine Backups to a New Drive
Plug the new backup drive into the Mac while keeping the existing backup drive attached. Open two new Finder windows by pressing Command-N twice while clicked into the Finder application.
In one of the Finder windows, navigate to the existing Time Machine backup drive (the drive that was just disabled) and select the Backups.backup folder by clicking on it. In the other window, navigate to the new drive.
Drag the Backups.backup folder into the new drive and wait for the folder to transfer completely to the new drive. This folder contains all existing Time Machine backups and corresponding information, so it will take a bit of time to transfer.
Note: If multiple Macs share the existing Time Machine drive, individual machine backups can be moved by creating a folder labeled Backups.backupdb on the new Time Machine drive, clicking into the existing Backups.backupdb folder on the existing drive, and manually dragging-and-dropping backups into the newly created folder.
Setting Up the New Time Machine Drive to Backup
Set up Time Machine to backup to the new drive. Click on the Time Machine icon from the Apple toolbar and click Open Time Machine Preferences from the drop-down menu.
Look towards the center of the window and click on the Select Disk button. From the drop-down menu, select the name of the new Time Machine backup drive and click the Use Disk button from the lower right-hand corner of the menu.
Time Machine will ask if it should stop using the old Time Machine backup drive to store backups, or if it should take turns backing up to your new and old drive. Select the option that works best for you and Time Machine will begin backing up to the new drive.
In this tutorial, I've shown you how to prepare a new backup drive for use with Time Machine and how to safely move the existing backups to a new drive.
For more Time Machine tips and tricks, check out the tutorials on Getting Started With Time Machine and How To Control Time Machine From Terminal.