If you've followed the directions so far, you've already tested the basic process of booting from a duplicate and restoring individual files from an archive. But in the event your data suffers serious damage, you will want to restore your duplicate, archive, or both onto your main hard disk. Read on for tips to help you through this process.

Repair or Erase Your Disk

If your startup disk (or another volume you've backed up) becomes unusable, you should not copy other files onto it while it's still in an unstable state. In case of serious trouble, the first thing you should do is start up your computer from another volume (a duplicate, a Mac OS X installation CD, or a bootable disk-utility CD such as Alsoft's DiskWarrior). Run Disk Utility or another disk-repair tool to fix any errors on your hard disk. If you are unable to fix the problems, or if they recur even after the utilities have done their best, use Disk Utility to erase the disk before attempting to restore your old files. (And by the way, if you're planning to restore all your files, it makes sense to erase the disk first, whether it appears to have any errors or not.)

Restore a Duplicate

If you've booted from your duplicate disk and erased your primary disk, restoring the duplicate onto the primary disk is a piece of cake.

Follow the same steps you normally would to create a duplicate, but choose your external disk as the source and your internal disk as the destination. When the duplicate is complete, use the Startup Disk pane of System Preferences to set your internal disk as the startup volume, and restart the computer. If all goes well, your Mac will boot properly from the freshly restored duplicate on your primary disk. Just be careful you don't confuse the backup with the original, especially if they have the same name.

Restore a CD/DVD Duplicate onto a Hard Disk

Let's say you have a duplicate of your hard disk, stored on a stack of CDs or DVDs. Now it's time to restore them onto your hard disk so you can boot from your duplicate, but your internal hard drive is the only one you have. So there's a problem: If you boot from the internal hard drive (assuming it even has a functioning system), you won't be able to restore the duplicate because that would overwrite files that are actively in use. On the other hand, if you have only one optical drive, you can't boot from that either, because you would then be unable to remove the boot CD/DVD to feed in the backup discs. What to do? The process is tedious, but it can be done. Follow these steps:

2. When the first installer screen appears, choose Installer > Open Disk Utility.

3. When Disk Utility opens, select your hard disk, click the Partition tab, and set up at least two partitions on the disk. (If your disk is already partitioned, you can skip this step.) Your goal is to have one partition that's large enough to hold the restored system and another that's large enough to hold a basic installation of Mac OS X. For the latter, a 5 GB partition should be adequate. (Caution: Partitioning your hard disk erases all the data on it.)

4. Quit Disk Utility, return to the installer, and install Mac OS X onto the newly created (small) partition. When asked to choose an installation type (the default is Easy Install), click Customize. Deselect everything except BSD Subsystem. Now proceed with the installation.

6.Reinstall your backup software onto the small partition that is currently functioning as your startup volume.

7.Use your software's duplication or restore feature to copy your duplicate from your CDs or DVDs onto the larger partition of your hard disk.

8.Use the Startup Disk pane of System Preferences to select your freshly restored volume as the startup disk, and restart your computer.

You've now restored your duplicate from optical discs to your hard disk.

Restore Archived Files

If you restored files from a duplicate (rather than from a full archive), once your primary hard disk is fully functional, your last step is to update it with the latest versions of files stored in your archive.
If your backup software has a snapshot feature, you should be able to select your most recent update and restore all the files from that date to their original locations. If your software uses differential additive archives, you must first restore the original, full archive backup and then restore the files from the most recent update.
If your backup software creates additive incremental archivesbut without a snapshot featureyou must again start by restoring the original, full archive backup. Then, step through each day's update, copying its files into their original locations (overwriting the older versions). Depending on how many files have changed and how long it's been since your last backup, this could be a lengthy process.

Note
If you've chosen to maintain a full archive and your archive backup was updated more recently than your duplicate was, you may opt to restore your archive directly. To restore a full archive:

Your Mac should boot properly from the freshly restored archive. (If it does not, follow the procedure outlined previously to restore your duplicate, and then restore your newer archived files.