My internal drive is suffering hardware failure, so I bought OS X Snow Leopard (to upgrade my iMac from Leopard), a new drive, and a cheap external USB 2.0 enclosure. My plan is to install a clean copy of Snow Leopard on the new drive as an external drive, restore a time-machine backup to it, and then finally swap the new drive into the iMac.

The main reason I'm doing it in this order, instead of just putting the drive in first, is timing. It's easier to install OS X on a fresh drive and restore the time machine backup during the week, when I have less time to mess with it, because those are fairly hands-off activities. I plan to do the drive swap this weekend when I have time for it, as I hear it is a fairly involved process to replace the internal drive on an iMac.

4 Answers 4


I've done this several times and never had a problem. Just make certain your external drive uses the correct partition scheme (GUID for Intel Macs) and format.

I once forgot to change the partition scheme and, as a result, couldn't run firmware updates until I reformatted the drive.

  • Very cool. For Snow Leopard, Disk Utility defaulted to making the scheme "GUID" when I partitioned it last night (I think because 10.6 requires an Intel Mac). Commented Feb 8, 2012 at 17:19
  • 1
    IIRC the Snow Leopard installer will refuse to install on disks that aren't in the GUID partition scheme. Probably to avoid this exact problem... Commented Feb 8, 2012 at 22:09
  • You may be correct. It's possible I had the problem back in the days of 10.5.
    – jaberg
    Commented Feb 9, 2012 at 8:09
  • Don't forget to turn on owners (vsdbutil -a)
    – w00t
    Commented Feb 14, 2012 at 20:55

After going through this same type of issue, I'd suggest using an approach of getting a new external drive, migrating your programs and data then installing it as you suggested. Afterwards, I'd go ahead and do any software updates you had planned.

This entire process is outlined at Other World Computing (www.macsales.com). you can buy the drive, get the transfer software (carbon copy cloner) and instructions on how to do it. I used this process twice and it worked great.


It is fine, I have done this countless times when I moved to SSD, just remember to go to Preferences --> Startup Disk and select the correct boot up drive after swapping. You only need to do this once otherwise you'll notice the boot sequence takes longer


For posterity, and for anyone else that runs into the same issue as me, here is the general steps I followed, and other important notes:

  • Alsoft DiskWarrior ($99) was an invaluable tool for rebuilding the directory structure on the failing drive when Disk Utility tells you that the drive is unrepairable. It let me restore the drive to copy recent files that hadn't made it to my Time Machine backup yet.
  • I purchased a new drive and cheap $10 external case from Otherworld Computing. I liked dealing with them because they are very Mac-centric, and have tools to select your exact model Mac to be sure the drive will work with yours. You can certainly use other vendors, but make sure the drive is compatible with your Mac!
  • I put the new drive in the external case, and bought a copy of OS X Snow Leopard (you can pick it up for under $29 single-user, or $49 family pack in the Apple Store). This was handy, as we had misplaced our original install disks, so otherwise had no way to format the new drive and copy the Time Machine backup over to it. Plus now we can upgrade to 10.6, of course.

  • If you are not comfortable with working inside a computer, you may want to find a friend or repair shop to help you with opening up the computer to replace the drive.

  • Several guides are available on YouTube and on the internet for opening up an iMac and replacing the drive. The key is, make sure you look up the guide for the correct model iMac that you have. If you are not sure what exact model iMac you have, you can use a site like Wikipedia to look it up and get your model number (you probably also need this to order your new hard drive, forgot to mention that!).
  • Don't forget proper static precautions when doing surgery on your Mac!
  • Hopefully once you succeed, then the first thing you should do is make a back up of your new drive.
  • Now I was free to finally do the 10.6 upgrade, with a new drive and freshly backed-up contents.
  • I'll likely keep the spare external $10 case handy, either to pull forgotten data off the old failed drive, or to buy and install a new, larger backup drive down the road.

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