It's a law of the universe. Sooner or later, Time Machine backups expand to fill all available space on a hard drive. It's actually a capability that we're glad Time Machine possesses. By using all available space, Time Machine can keep backups of our work going back as far as…well, as far as there's available space.
Eventually, though, you may decide you need more room for your Time Machine backups, and want to move them to a larger hard drive. You may need more room for two primary reasons. First, the amount of data you store on your Mac has grown over time, as you've added more applications and created and saved more documents. At some point, you may outgrow the amount of space available on your original Time Machine hard drive.
The other common reason for needing more room is a desire to store more data history. The more data history you can store, the farther back in time you can retrieve a file. Time Machine will obligingly save multiple generations of documents or other data, as long as you have enough room to accommodate them. But once the hard drive fills up, Time Machine will purge older backups to ensure you have room for the most current data.
Moving Time Machine to a New Hard Drive
Starting with Snow Leopard (OS X 10.6.x), Apple simplified what's required to successfully transfer a Time Machine backup. If you follow the steps below, you can move your current Time Machine backup to a new disk. Time Machine will then have enough room to save a larger number of backups, until it eventually fills up the available space on the new drive.
Preparing the New Hard Drive to Be Used for Time Machine
- Make sure your new hard drive is connected to your Mac, either internally or externally.
- Start up your Mac.
- Launch Disk Utility, located at /applications/utilities/.
- Select the new hard drive from the list of disks and volumes in the left side of the Disk Utility window. Be sure to select the disk, not the volume. The disk will usually include its size and possibly its manufacturer as part of its name. The volume will usually have a simpler name; the volume is also what shows up on your Mac's desktop.
- Time Machine drives need to be formatted with the GUID Partition Table. You can verify a drive's format type by checking the Partition Map Scheme entry at the bottom of the Disk Utility window. It should say GUID Partition Table. If it doesn't, you will need to the format the new drive.
WARNING: Formatting the hard drive will erase any data on the drive.
To format the new hard drive, follow the instructions in the guide below, and then return to this guide:
If you want the new hard drive to have multiple partitions, follow the instructions in the guide below, and then return to this guide:
- Once you finish formatting or partitioning the new hard drive, it will mount on your Mac's desktop.
- Right-click the new hard drive icon on the desktop, and select Get Info from the pop-up menu.
- Make sure that 'Ignore ownership on this volume' isn't checked. You'll find this check box at the bottom of the Get Info window.
- To change the 'Ignore ownership on this volume' you will first have to click the padlock icon located in the bottom right corner of the Get Info window.
- When prompted, supply an administrators username and password. You can now make the changes.
Transferring Your Time Machine Backup to a New Hard Drive
- Launch System Preferences by clicking the System Preferences icon in the Dock, or selecting System Preferences from the Apple menu.
- Select the Time Machine preference pane.
- Slide the Time Machine switch to Off.
- Return to the Finder and browse to the location of your current Time Machine backup.
- Click and drag the Backups.backupdb folder to the new hard drive.
- If asked, supply an administrator name and password.
- The copying process will start. This can take a while, depending on the size of your current Time Machine backup.
Selecting the New Hard Drive for Time Machine's Use
- Once the copying is complete, return to the Time Machine preference pane and click the Select Disk button.
- Select the new hard disk from the list and click the Use for Backup button.
- Time Machine will turn back on.
That's all there is to it. You're ready to continue using Time Machine on your new, spacious hard drive, and you didn't lose any of the Time Machine data from the old drive.