Originally Posted By: ryck
Anyway, I tired everything including a complete erasure of the backup drive (using Disk Tool) and a fresh recording of the backup using Super Duper. To erase I had to try a couple of times as the dialogue box said it could not unmount the drive.

  1. Did you erase the drive or the volume on the drive? The way to erase the drive is to repartition the drive which in addition to rebuilding the file directories also rebuilds the GUID partition table.
  2. The fact TechTool took so long would lead me to suspect it was having problems reading some disk sectors an indication of a disk headed toward complete failure. Since you have TechTool Pro….
    1. run the TechTool S.M.A.R.T. test — it is far more informative than the SMART test in Disk Utility and most other utilities as it reports the individual tests and not just the aggregate results.
    2. run a full surface scan. It takes a l-o-n-g time but it is the best indicator of impending drive failure.
  3. For reasons I was never able to deduce I went through a spell where option booting only indicated the normal boot drive unless I did a cold boot (full shut down and then restart). Aggravatingly enough that "fixed" itself after a couple of months. You might try that

Originally Posted By: ryck
It appears the iMac now may think the Super Duper Backup Drive is the main drive. With the SD Backup on the desktop I located a folder, created a new folder inside it, and stored some files. However, when I returned to the new folder, it was not on my main drive. It was on the Super Duper Backup drive.

If you look in System Preferences > Startup Disk, what does it think the startup drive is?


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