RE: Time Machine Error: Backup Volume is Read Only?
I just got back from an appointment at the Apple Store's Genius Bar. I found out what was causing my trouble. Hopefully this will help others:
The guy who was helping me ran diagnostics but could not find logs to determine what caused the backup failure. I had already reformatted and backed up since the read only/reformat error. There's still no explanation as to why there were no logs.
Anyway, I told him it would be okay to reformat and do another backup which he wanted to do to remove the master boot block which has been known to be the culprit on issues with Mac backup failures. Unfortunately, my device is a 250 GB USB Western Digital portable drive which is extremely slow for the first backup. I have about 120 GB of data to back up. So, I told him to stop the backup and I will finish it at home and come back if there is another issue.
This is when the trouble began, it was taking a long time to shutdown. The laptop was at the stage where all you see is the OS X screen without the menu, desktop items, or dock and the little circling hashes indicating it was still trying to shutdown. This went on for over 10 minutes. I then told the Apple tech that this happened after the software update which required a reboot and that I just shut off the system with the power button. He explained, and I should have known better, that the system was trying to unmount the disk and this is what caused the disk failures.
Sure enough when the tech stopped the shutdown and restarted the computer in diagnostic mode, the error reappeared. He reformatted the disk and the computer successfully shutdown.
Some of you may be wiser than I but I normally do this for my PC which takes forever to shutdown but of course it may not be accessing the disk when I shut it down. Anyway, this is a change I will need to make with my Mac. Unfortunately, I have no idea how long the unmount process could possibly take; ten minutes seems like an inordinately long period of time.