Time Machine Backup


Today’s Question: I use Time Machine on my iMac for backups. The iMac has external LaCie Hard Drives. Are the external drives included by Time Machine in its backup sequence?

Tim’s Quick Answer: No, by default Time Machine does not backup your external drives. However, you can choose to include external hard drives as part of your Time Machine backup if you prefer.

More Detail: Time Machine provides an automated backup solution for Macintosh computers. To the extent possible based on the space available on the hard drive you are using to backup your computer, Time Machine will create hourly backups for the past 24 hours, daily backups for the past month, and weekly backups beyond that. When the drive gets full older backups will be deleted. Therefore, depending on the storage capacity of the external drive you’re using for your Time Machine backup, and the amount of data being backed up, your oldest backup may not be particularly old.

By default Time Machine will exclude any connected external hard drives from the backup, so that only the internal hard drives are being backed up. However, you can change this setting in the Options for Time Machine.

To get started, connect both the hard drive you’re using for your Time Machine backup and the external hard drives you want Time Machine to include in the backup. Then click on the Apple logo at the far left of the menu bar and choose System Preferences. In the System Preferences window choose Time Machine. Then click the Options button to bring up a dialog that will show you the external hard drives that are currently excluded from your Time Machine backup.

Select any of the external hard drives from the list that you want to include in your Time Machine backup, and click the “minus” button to remove that drive from the exclusion list. Click Save, and your settings will be updated.

Keep in mind that if you want to backup your internal drives and one or more external drives as part of your Time Machine backup, you will need to have an external hard drive with enough capacity to backup all of the data you are including as part of your backup. Furthermore, since Time Machine is designed to preserve older versions of files as well, you ideally want to use an external hard drive for Time Machine that includes considerably more space than the amount of data you are backing up.