Step one would be to try and make a bootable backup of your current boot volume and then backups of any data volumes. Use Carbon Copy Cloner or SuperDuper!.
Step two, if you sprang for the AppleCare Protection Plan, would be to request onsite replacement.
Step three is to have them do the replacement, ensure that it works as advertised afterwards, wipe the HD, partition the HD as desired, and restore the bootable backup.
Step four is to do a search in these communities for imac AND HD AND replacement and peruse the results (sort by date).
Thanks for your reply.
Between a quarterly disk in my safety deposit, Time Machine, and a recent CCC clone I'm completely covered as far as backups. But I think a last-minute re-clone is the best option for speedy and complete post-replacement restoring.
I did spring for Apple Care for this machine. I can't find the receipt, but I think it has expired... wait checking with the mother ship, here-- Apple says my machine is still covered. Woo-hoo! So... yeah, brilliant, everything points to on-site as the way-superior alternative. I'll get right on it.
The AppleCare route went really well, as good as it can get. (5 Gold Stars for efficiency and minimized downtime!) Only about 40 minutes entrance-to-exit to replace the drive, thanks to a skilled and personable technician who came to my door, bang on-time. He initiated the first OS install and left --with my thanks-- as soon as it was under way, clearly working. Followed by about 7 hours to get back to where I was (10.7) and do a TimeMachine restore of ~350GB. That's on top of about a day of preps, including erasing the disk-to-be-replaced and overwriting it with zeros, twice.
Hats off to the Apple ME's for a really elegant design of a very complex set of computer guts, enabling a very quick open-replace-close process!
So far, 1 day in, everything seems to work, including/especially two vital Adobe-licensed apps. The only glitch I've seen so far is a purchased iTunes cut that won't play.
• The AppleCare rep tried to steer me toward "carry it in" service at a Genius Bar or service depot. Once I asked "Can't you send someone by to do it?" the process went very smoothly and quickly to the on-site visit.
• DiskUtility's "Erase Free Space" function gave me the worst time-to-completion estimates I've seen from an Apple app. I couldn't find estimates ahead of time. If I could have anticipated the time necessary to do a complete ~1TB 3-pass erase, I would have allowed enough time to do it. No reflection on the tech service intended, I'm confident they'll handle the old HD with discretion, just my extra caution.
• The restore roadmap was a bit obscure past the instructions, "re-install MacOS from the DVD that came with your system". That was 10.6. Did I need bring it up to 10.6.8? Could I go directly from 10.6 to 10.7? I think an install of 10.7 was necessary, if only to create the recovery partition and the bootable system and utilities inside it; I don't think TimeMachine can do that, though it seemed to be able to recreate my existing configuration in all other respects. I did not need to bring 10.7 up to 10.7.5, I know now, as the TM full-restore says it erased the target before restoring. (Fortunately, I've never had reason to experience a full TM restore before!) Knowing more might have shaved some time from the post new-HD process and made it a bit less tense.
• After the restore, I was a bit surprised that mail.app had to do a big rebuild before it would work; I wish I had known about that before-hand. Not surprised at Spotlight re-indexing. Spotlight gave a very good explanation of what was going on -- good job!
• App Store would not re-download my previous 10.7 purchase. Fortunately, I had made an ESD and I could install from that. (Why wouldn't it re-download? What would I have done without an ESD? A trip to Apple store to get a ESD-thumb-drive?) Note:I see that iMac models a bit newer than mine seem to have a much more robust recover-from-the-net procedure available. Cool!
To repeat: .... as good as it can get!
Don't like to hear "flakey" in reference to TM --and that's not my experience-- but that's another discussion.
Restoration from a TM needs to be done before relying on it, since the TM backup isn't bootable or otherwise testable. There are too many posts in these forums wherein the TM restoration failed, that's why I consider it flakey; whereas, a bootable clone (I only use CCC) is immediately testable by booting into it.