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Summary:

Whether your hard drive has failed or your OS has become corrupt, you may occasionally have to reinstall the Mac OS.  Fortunately, Apple does a beautiful job of making installing or reinstalling your operating system relatively painless compared to our Windows brethren. Unfortunately, it’s still a […]

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Whether your hard drive has failed or your OS has become corrupt, you may occasionally have to reinstall the Mac OS.  Fortunately, Apple does a beautiful job of making installing or reinstalling your operating system relatively painless compared to our Windows brethren. Unfortunately, it’s still a painfully slow process running off a DVD. Not to mention, optical media can get scratched easily (one of the reasons for the long install times is Apple’s optical media verification).

To solve this problem, I recommend backing up your Mac OS installation DVD to a hard drive. Doing so protects it and allows you to install the OS quickly, as well as run Disk Utility on your main drive or reset a password. I keep a hard drive with Leopard and Snow Leopard installers so I can reinstall or repair multiple OS versions easily.

Getting Started

To start, you’ll need a copy of Snow Leopard (or whatever OS version you want to install). Open Disk Utility, which is typically found in /Applications/Utilities. On the left-hand side you see your disk appear as “Mac OS X Install DVD.” Go ahead and click the New Image icon to make a copy of the DVD. Save the file at your preferred location (I have a Archive folder on my hard drive for installer disks).

Prepare the Drive

Now that you have a digital copy of your installer, the next step is to prepare the hard drive you will use for the restoration. In this example, I connected an old 160GB hard drive from my MacBook into an external case. I’m dividing this particular one into three partitions: one for Leopard, one for Snow Leopard, and one for other installers such as iLife. I could put Tiger on it, but I get few requests for that OS. Since I want this to boot Intel-based Macs, I’m going to click options and make sure GUID Partition is selected. I’m making the partitions 10GB, but you can choose any size above 8.5GB to play it safe. You could also use a USB flash drive, but those can be slow. I suggest sticking with a hard drive-based solution for speed reasons.

Restore the Image

After preparing your drive, you’ll need to restore the image to your hard drive partition. Click the Restore tab in Disk Utility. For Source, click Image… and choose that image you created earlier. For Destination, drag the partition you want to restore the OS to, then click “Restore.”

You might get an error saying, “Restore Failure: Could not find any scan information. The source image needs to imagescanned before it can be restored.” If you get this message, go ahead and go to the Images menu and choose “Scan Image for Restore.” Choose the disk image you are using as source. Now click Restore; it shouldn’t ask again.

In my example, I’ll do the same for the second partition and put Leopard on it. Both partitions will be named Mac OS X Install DVD. That can be confusing on boot, so I suggest you copy the icon from each installer CD and paste it onto the respective hard disk volumes. You’ll easily be able to tell from the icon alone which OS you are installing. If you hold down Option during the startup of your Mac, you’ll be presented with those icons as well so you know which installer will boot, and you can go ahead and install the Mac OS the normal way.

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  1. Can you back it up as well to a external drive so that you have a second copy and while I’m on the subject, can you make your Time Machine backup bootable?

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    1. You can’t boot from TimeMachine as far as I know.
      But you can use Carbon Copy Cloner instead. It’s free to use and free of donating any amount for their great job.

      And with those Bu’s you can boot on almost every mac.

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  2. I have Carbon Copy Cloner but don’t own Bu’s since their price is still to expensive for what you get.

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  3. A few things.

    - You can rename your installer boot partitions something like “Leopard Installer” and “Snow Leopard Installer.” The Installer doesn’t care what the volume name is that it’s installing from. The pasting of the icons is a nice touch (and I do the same), but less of a differentiator than the volume name.

    - Did you create your disk image from a 10.5 or 10.6 OS? I ask because I’ve had lots of problems using 10.6′s Disk Utility to create ASR images that restore properly (yes, even after scanning the image for restore). I’ve yet to be able to make a digital image of a Snow Leopard installer using Snow Leopard’s Disk Utility. I’ve had to fall back to a Leopard box and using Leopard’s Disk Utility to be able to create an image that restores properly to a volume for installation. I suspect it’s a bug in 10.6′s Disk Utility and have seen posts referencing this problem on Apple’s boards and on the Mac sysadmin mailing lists.

    - If you’re making a bootable Leopard installer, you can format your volume as Apple Partition Map, which will allow you to boot older PPC Macs. As you’ve outlined in your article, you’re limiting this installation to Intel Macs only (which is fine if you’re only doing a Snow Leopard installer as it’s Intel-only, of course). Just a data point. I carry two different HDs–one formatted with a Leopard Installer on an APM volume, and a 2nd one formatted as GUID with a Snow Leopard Installer.

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  4. Al Winchester Thursday, March 25, 2010

    This works well for the Snow Leopard Install DVD. I have been trying without success to do the same thing with a .iso file. Any thoughts?

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    1. I don’t the procedure will be different for ISO files. Disk Utility treats DMGs and ISOs in a similar way once they’ve been mounted.

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  5. Michael Rosenthal Sunday, April 25, 2010

    You’re making this way too complicated. All you have to do in Disk Utility is Restore using the Install Disk as the source and the external drive partition as the Destination. I recall that this one step process takes about 30 minutes and you’re done.

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  6. I have done all of this exactly as you said. But when I get to the part where I need to “scan image for restore” in disk utility, I keep getting a message that says “unable to scan, invalid argument”
    What does that mean and is there any way around it?

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    1. Make sure that you mount the iso on your desktop by opening it and then when you are doing restore right click on the opened .iso and set as source.

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  7. Hi, here might be a solution to the restore and scan images problem for snow leopard.
    Create the image with DU and then restore it in the terminal with:

    $sudo asr –noverify –source /Volumes/xxx/osx_leopard_snow.dmg –target /Volumes/osxleopardsnow

    source:
    http://www.onpaws.com/2009/10/fixing-disk-utility-image-restore/

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    1. Thanks suuuuuuper, you helped me with an image that failed to verify :)

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