We will first create a new partition on the backup drive, then clone the install DVD to this partition and finally boot from the external hard disk.

Add new partition

First of all, we need a new partition on the backup drive to boot from. Thanks to the OS X disk utility, this is quite easy. I use an SATA drive with 1 TB capacity living in a Sharkoon Quickport Pro connected via USB. So fire up disk utility, select your backup drive and open the Partition tab.

As you can see, there is already plenty of space used on the drive, but that’s no problem at all, as disk utility can resize partitions. Just drag the lower right corner of the partition upwards until it frees the space you need. I set up a 10 GB partition. Finally apply the changes.

Clone Install DVD to new partition

Next we clone the install DVD (Snow Leopard in my case) to the new partition. Insert the DVD, select your new partition in disk utility and go to Restore. Drag the Mac OS X Install DVD to source and your new partition on the backup drive to target. Then click on restore and wait.

That’s all you need to do. Let’s try to boot.

Boot from the backup drive

Finally, reboot your Mac and hold down option key on startup. If everything went well, the new partition appears in the list of bootable devices. Select it and be amazed how fast you enter the OS X setup.