Chosen Solution
I’m trying to install El Capitan to an old 2008 Mac Pro. I have tried a known good HDD, rolled back the date and time but it wont unmount, says it can’t write to the last block of the device, do you know what could be causing the issue?
What is the make and model of the HDD? Often times this type of error happens when the drive is to fast for the given systems SATA port. As an example you put in a fixed speed SATA III (6.0Gbps) drive into a SATA II (3.0Gbps) I/O port in your system.
