Information Technology Reference
4. On the Erase view, click Erase, and confirm that you really want
to do that. Disk Utility erases the disk.
5. Follow the steps in Create a Bootable Duplicate to copy the contents
of your duplicate back onto your internal disk; except in this case,
you'll choose the external disk containing your duplicate as the
source and your internal disk as the destination.
6. If your versioned backup software (Time Machine or otherwise)
ran after the most recent update of your bootable duplicate, you
may want to use it now to copy any new or changed files back to
your main disk. Unfortunately, most backup software (including
Time Machine and CrashPlan) has no way to select for restoration
only files that changed after a specified date and time—namely,
those that changed and were backed up after you last updated
your bootable duplicate. In general, you'll have to find all those
After you restore a bootable duplicate in this manner, Time Machine
may conclude that all the files on your disk have changed and try to
create an additional copy of all of them. Read the sidebar Restarting
Time Machine Backups after a Restore , earlier, for more details and
a possible solution.
Recovering from the Loss of a Backup Drive
What if you had just one drive with a bootable duplicate and
versioned backups—relying on an Internet backup service for a
secondary backup—and you lose both your internal drive and your
external backup drive? Restoration is harder, but still possible.
On a new or freshly erased drive, (re)install Mac OS X; set it up with
the same username and password you used previously. Next, install
your key applications from discs or downloads—including your
Internet backup utility! Use that to restore the files from your online
backup. This can take quite a while, but as long as you stored the
entire contents of your home folder online, the end result should be
a restoration of your system to nearly the state it was in previously.