MacUpgrades Time Machine FAQ

What is Time Machine?

Time Machine is a piece of sophisticated incremental backup software with a powerful rollback facility, designed for and integrated into Mac OS X 10.5 (Leopard).

After taking an initial complete backup of the system to an external or additional hard drive, time machine takes a snapshot of changes every hour assuming the backup drive is connected. You can then at any point recover either individual files or folders, or do a complete system restore, from a choice of earlier points.

The software allows you to choose to restore from any hour in the last 24 hours, any day in the past month, and any week until the backup drive runs out of space and older backups are discarded.

This means time machine avoids a major problem with more basic backup systems, since it allows you to recover deleted or corrupted files even if the unwanted changes have already been backed up.

Apple's own overview of Time Machine can be found here.

How to Setup Time Machine

Get an external hard drive and use Disk Utility to erase (format) the disk in "Mac OS Extended (Journaled)" format (also known as HFS+). It is well worth it at this point to check the partition map, since some external drives will be supplied with an MBR (Master Boot Record) partition type, which will cause problems - see Apple's site here for details of the issue and instructions on changing the partition type.

If you do not already have a Time Machine drive configured, you should get a message when you connect a new external drive, asking if you want to use the new drive for Time Machine. Alternatively you can open the Time Machine preferences from within the main System Preferences panel, and use it to nominate the drive.

Time Machine will then do its initial backup - this may take several hours, depending on the amount of data you have. Once this is complete, Time Machine will take incremental backups of changes every hour, assuming the backup disk is connected. NB: If a user on the computer uses File Vault to encrypt their user folder, that user folder is only backed up when that user is logged out.

You can access Time Machine preferences from the main System Preferences panel, and use this to exclude certain files (or entire volumes) from backup - this can be useful if you are making frequent changes to a very large file, and want to prevent Time Machine backing it up every hour. Or to prevent Time Machine from backing up unimportant or already backed up information to save disk space.

How to Restore from Time Machine

To restore specific files and folders, click the Time Machine icon in the dock (or in the Applications folder). You can navigate Time Machine to browse between any of the backup points it has saved (hourly points for the last 24 hours, daily points for the last month, and weekly points going back as far as there is space for on the backup drive), and browse there for the file or folder you need. You can also use Spotlight to help you search through your backup. When you restore a file or folder, it will return to its original place on your hard drive (prompting you to recreate any containing folders if needed).

You can also restore your entire system from any backup point - very useful after a drive failure or upgrade. To do this, boot your Mac from the install disk and get to the point where it asks you to choose a target drive. If you have fitted a new drive, you will not be able to see it here if it is unformatted, see here for instructions on using Disk Utility to format the drive.

When you can see your new hard drive as a valid target drive, go to the Utilities menu and choose Restore System From Backup. You can then choose from any backup point, choose your new hard drive as the target, and your backed up system will be restored onto your new drive.

There are some areas excluded from Time Machine backups, such as Spotlight caches and log files, this generally should not cause a problem for most users but can in some specific cases. A list of excluded files can be found here.

Troubleshooting Time Machine

If you are having problems with Time Machine, Apple provides detailed information to help troubleshoot them. See here and here.

What is Time Capsule?

Apple's Time Capsule product is a combined 802.11n wireless router and network attached storage (NAS) hard drive.

It is designed to integrate with the Time Machine backup software, but it is not required since Time Machine will work with any external hard drive.

What are the disadvantages of Time Machine

Time machine is an powerful and full-featured backup application, but it does have some drawbacks:

Because it is a complex incremental backup system, the Time Machine drive is not itself bootable, unlike a full disk clone done with software such as Carbon Copy Cloner. This means that if you have a drive failure, you cannot use the machine until you have replaced the hard drive and done a restore - with a cloned drive you can boot from the backup directly and work on it as you did with the original. However a full disk clone takes many hours to complete, and even an incremental clone doesn't have the multiple backup points that are one of Time Machine's strongest features.

Since it is not bootable you also cannot test your backup without actually doing a restore from it. One of the more catastrophic computer horror stories involves a fault with a backup system that is not spotted until the backup is needed.

Time Machine does not backup everything - certain things like log files are excluded (they would consume a large amount of disk space on your Time Machine drive, since log files change frequently and can be very large). The excluded files shouldn't cause problems, but shouldn't isn't wont.

For these reasons, if you are doing a planned migration - for example upgrading your boot drive to one of a larger capacity, you may want to go the cloning route instead. See our Drive Cloning Guide for full details.