Originally Posted By: MG2009
I would be happy to leave the SSD for the OS and the HDD separate for the DATA . . . However, the HDD cannot be used AS IS. It cannot be formatted or written to because it "cannot be written to the last block" and any attempt at formatting or erasing "fails."

Which is why I suggested intentionally breaking the already broken Fusion Drive on the theory that might resolve the issue preventing the HDD from being initialized. It is one of those it can't hurt and might help procedures and would only take a few minutes to try. There are two keys to doing this successfully
  1. Be sure you are booted from the Internet Recovery Drive
    • Option+Command+R
    • You are prompted to log onto a network
  2. you enter the commands exactly as shown in the article

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein