How to setup an external drive for installing OSX

I have been setting up an external hard disk (a Western Digital Passport 250GB) since becoming a Mac Developer. Despite having a Mac Pro, A Mac Book Pro and a Mac Mini, I don't have a spare Mac for testing things like new releases of the next Mac OS that you get as part of the developer program.
I have found various people on the internet who have instructions on how to copy your install DVD or image to a hard disk partition and then install the OS onto an external drive which you can then boot from. Doing it this way means you can test the new OS without touching the internal drive, very useful.
I have decided to show you how I do the whole process in one blog post so I hope you find it useful.

Step 1: Partition your external hard drive.
WARNING: Either use a new drive or one that you have backed up because this process will erase any data you had one you drive previously.
Open Disc Utility (Applications->Utilities->Disk Utility

Create as many partitions as you have install DVDs or image files. I created 3 8GB partitions. One for OSX 10.5.5, one for OSX 10.6 and one for OSX Server 10.6 The area of the disk that is left is where I will install the OS. Make sure you use the GUID Partition Table scheme, the ensures that all the drives are viewable and bootable when you start your Mac with the drive attached.

Step 2: Restore the DVD and/or the disk image to a partition.
Select the source by either clicking and dragging the source DVD or image from the left pain or click the Image... button to select the desired image file.
Then click and drag the destination partition to the Destination field.

Now click the Restore button. A warning message will popup telling you that the destination will be erased, click Erase to continue. You will then be most likely to be asked for your admin credentials to continue. This will start the restore process, it will take a while (around an hour on my Mac Pro when restoring from the DVD less from an image file).

Once the restore has completed you will see the installation disk popup.

Step 3: Installing OSX to an external drive.
Shut down the Mac. Connect your external drive with the installation images to the Mac.

In part 2 of this post we'll go through the install process.

Comments

[Paul Shadwell]

Tim, that's a good question. I will give it a try and let you know.

John, yes it's been a long time coming but I will try and finish soon.

[john pfeffer]

Great first part... It mentions the rest in Part 2... where is that part of the post?

thanks

[tim]

Do you have to partition the external hard drive to make this work? Can I just make a disk image on the external drive and go from there?

[Jane]

Step by step instructions like these are so useful for "newbs" like myself. Thanks for taking the time to be so thorough in your descriptions of this useful OS X installation technique.