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Time Machine With Multiple Drives - How to Use Two or More Backup Drives

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Time Machine Tips - How to Set Up a Reliable Backup System for Your Mac
Time Machine Tips - How to Set Up a Reliable Backup System for Your Mac

With the introduction of OS X Mountain Lion, Apple updated Time Machine to work more easily with multiple backup drives.

Screen shot courtesy of Coyote Moon, Inc.

Introduced with OS X 10.5 (Leopard), Time Machine is an easy-to-use backup system that has probably prevented more Mac users from losing sleep over lost work than most other backup options combined.

With the introduction of OS X Mountain Lion, Apple updated Time Machine to work more easily with multiple backup drives. You could use Time Machine with multiple backup drives before Mountain Lion came along, but it required a good deal of user intervention to make everything work. With OS X Mountain Lion and later, Time Machine retains its ease of use while providing a more robust backup solution by allowing you to easily assign multiple drives as Time Machine backup destinations.

The Benefits of Multiple Time Machine Drives

The primary benefit comes from the simple concept that one backup is never enough. Redundant backups ensure that should something go wrong with one backup, you have a second, or third, or fourth (you get the idea) backup from which to retrieve your data.

The concept of having multiple backups isn't new; it's been around for ages. In business, it's not uncommon to have backup systems that create two local backups that are used in rotation. The first may be for even-numbered days; the second for odd-numbered days. The idea is simple; if one backup goes bad for any reason, the second backup is only a day older. The most you would lose is a day's work. Many businesses also maintain an off-site backup; in case of fire, the business won't lose all of its data if there's a copy safe in another location. These are actual, physical backups; the idea of off-site backups long preceded cloud computing.

Backup systems can get very elaborate, and we won't go into them in depth here. But Time Machine's ability to work with multiple backup drives gives you a great deal of flexibility in building a custom backup solution to meet your needs.

How to Build a Robust Time Machine Backup System

This guide will take you through the process of creating a three-drive backup system. Two drives will be used to attain a basic level of backup redundancy, while the third will be used for off-site backup storage.

We've chosen this example setup not because it's ideal, or will meet everyone's needs. We chose this configuration because it will show you how to use Time Machine's new support for multiple drives, and its ability to work seamlessly with drives that are only present temporarily, such as off-site backup drives.

What You Need

  • A Mac running OS X Mountain Lion or later.

  • Three drives. Each drive must be large enough to store the data you have on your Mac, and then some. The more space available on the backup drives, the more historical Time Machine data they can hold.

  • If you only want to create a two-drive backup system, you can still use this guide. Just modify the number of drives from three to two as you work through the instructions.

  • Types of drives: That's up to you. This guide will work for local internal drives, external drives, Time Capsule drives, and network drives that are supported by Time Machine.

  • About an hour of your active time to set up the Time Machine backup system, and a good deal more time to perform the first set of backups.
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