Chosen Solution
Replaced my Seagate 500 GB with the WD 1 TB, and the drive doesn’t read. Get the ? mark. The OS was preloaded using an external HD case. Put back the 1TB in the case, it reads but it doesn’t read the ITB internally. Is it that the drive isn’t compatible? HELP
Most likely is that the drive was not formatted correctly to GUID and Mac OS X extended. A mac will boot from an external disk that say is formatted FAT, but will not do it internally. Also, the hard drives in the 2011 had Apple priority heat sensors. Changing brands of hard drives will cause run away fan issues. OWC has addressed this issue with this fix: OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade https://eshop.macsales.com/item/OWC/DIDI…
