Unable to install OS X Yosemite on Mid-2011 iMac

I’ve been unable to install Yosemite on a mid-2011 iMac. Apple are aware, but so far haven’t been able to help. Here’s the story.

2014-10-17 Update → Although I sent a RADAR bug report, Apple weren’t able to fix this before releasing the final version of Yosemite. I tried installing that version on our iMac, and it again failed, wiping out the startup drive. Hopefully this doesn’t affect too many others.

2014-10-12 Update → I’ve now determined that the problem is not with the SSD, but something related to the machine itself. Instead of installing Yosemite on the SSD, I tried installing it on the backup drive, an internal 1TB Hitachi drive. The exact same thing happened — Upon reboot, the startup progress bar proceeded about half-way across, and then I got the “no-system” icon. When trying to restore the backup drive from the SSD, I got the same “volume is unreadable” error (requiring reinitialization) and then when trying to restore the backup drive, I got the same “OS X reports read/write errors on the drive” from Carbon Copy Cloner. So again, exactly the same experience when trying to install on the backup drive as I had when installing on the primary SSD.

Original post → I’ve been unable to install the Mac OS X 10.10 Yosemite GM 1 on my mid-2011 27" iMac, and wanted to document the problem here in case others are running into the same issue. (Maybe somebody will have a solution!)

The startup drive is an Apple SSD. It’s not the original SSD delivered with the iMac, but rather a replacement unit installed by technicians at the Apple Store when the original SSD died last year:

After running the installer, when the computer reboots, the progress bar proceeds about 75% across, and then the circle-with-a-line-through-it icon appears on the screen, indicating that no bootable system exists on the startup drive.

When I then boot from the backup drive (an internal 1TB hard disk), a “This disk is unrecognized. Would you like to format it?” warning appears related to the SSD, requiring me to completely reformat it.

Then, when I use Carbon Copy Cloner to try to restore the startup SSD from the backup, it displays an error along the lines of “The OS is reporting read/write problems with this drive. Do you really wish to continue?”. I do continue, and the restore completes, the computer can boot and run without problems again from the SSD.

I haven’t found much on the internet about this, but one article in particular would seem to indicate that the SSD isn’t compatible with Yosemite due to Yosemite-related new security systems. However, booting into safe mode and running the Terminal commands listed in the article didn’t solve the problem on my system.