iMac refuses to boot, Disk Utility always says there are drive errors it can't repair -- what to do?

Question

This is a follow on to the question I asked about replacing the hard drive in my iMac. The restore from TimeMachine finished and the machine still won't boot. Just the white screen, Apple logo and spinner. I booted to the Snow Leopard DVD and ran Disk Utility on it again -- and again Disk Utility told me:

Verify and Repair volume "Main"
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Invalid node structure
The volume Main could not be verified completely.
Volume repair complete.
Updating boot support partitions for the volume as required.
Error: Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

Is this drive dead? Seems odd I could restore to it if it's dead. Should I try an older backup from TimeMachine? Could the most recent backup be restoring something so corrupt to the disk that it's un-bootable after the restore?

Edit: SMART status for the drive was fine. No problems reported.

Edit: I restored from a TM backup that wasn't the latest. A few hours before that. It still won't boot, but I get a little further in the Repair Disk function now. Mean anything to anyone?

Verify and Repair volume "Main"
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Invalid sibling link
Rebuilding catalog B-tree.
Invalid key length
The volume Main could not be verified completely.
Volume repair complete.
Updating boot support partitions for the volume as required.
Error: Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

Update: it was an issue with my primary drive. It had something going on with that was preventing it from being boot-able. Replacing the drive (more or less) fixed the problem.

Answer 1

Having solved the problem I can answer my own question.

It was a problem with the iMac's internal hard drive. Scanning the drive after the fact revealed a whole host of bad sector errors. Not sure why I couldn't pick this stuff up when I was trying to restore to it.

In any case, even with a new drive installed in the machine I couldn't get the Utilities -> Restore method of restoring the machine from my TimeMachine drive to work. It did the same thing with a new drive: it's just hang forever on boot, no chime, just Apple logo and a spinner for hours and hours.

The solution was to do a clean OS X install from the OS X DVD (instead of using the Utilities -> Restore menu option to restore the machine). Then, on first boot, when you first log in to OS X it'll ask you if you want to restore this machine from a TimeMachine drive. I said "Yes" to this option, it found my TimeMachine drive, I selected all the available types of things to restore (System Settings, User Data, Applications and Other) and let it do its thing for a few hours.

And this time it worked. Reboots were fine. My data is there and intact. All is well.

Answer 2

It sounds like this is a file system issue, rather than a drive issue, and you're right to consider restoring to an older backup. Unfortunately it's going to be hit-and-miss for a while, until you find a backup that works.

Once you're able to restore to a working version, I would do as DiskUtility says and backup your files and reformat the drive/reinstall the operating system, then make a brand new Time Machine backup from that.

Likely, the drive is fine, it's only something to do with a corrupt backup.