I was trying to help my brother fix his computer: A pop up that comes up at login that will tell you that your startup disk is full, he logs in and the screen gets stuck without loading any files.
I boot into EFI (or whatever you want to call it), Some reading device fails so everything is read only, but accessible. I try to plug in a external hard drive to save some items before trying to simply re-install the system, I get "SAM Multimedia: Read or Write Failed ASC=0x11 ASCQ=0x00" something similar I don't remember the exact error code I do know ASCQ was 0x0 which seemed telling. So basically I could neither find nor mount the external hard drive.
I actually this multiple times, the first time the computer crashed in EFI when I tried to open his user file.
I tried running puppy dog linux: an OS that boots from CD and runs from RAM. a device called "sda1" shows up, It had a nested file: EFI/APPLE/EXTENSIONS/Firmware.scad. I couldn't find anything else. I don't know what to do I've never had to deal with this on my mac.