In short: If you have installed a SSD device from a 3rd party vendor to a Macbook ALWAYS disable tools for trim support in Mac OS X BEFORE resetting the NVRAM/PRAM for troubleshooting. Your Mac will stop during next startup with a stop-sign on grey background:
After the last reboot on my Macbook Pro (late 2011) I have seen this error for the first time.
I tried the common troubleshooting steps (safe boot, reset SMC and repair disk/filesystem with Disk Utility) with no success. The safe boot stopped with the message “waiting for root device”.
At next I removed the SSD from the Macbook and could successfully boot from another SSD with OS X installed. So I tried to connect the estimated defective SSD with a SATA/USB Adapter to check if I can backup some files.
Surprise – the system booted automatically from my SSD when connected via USB.
I had no luck finding some tips for further troubleshooting. I finally decided to install the SSD back to the Macbook and re-install the OS with a bootable USB install device. All data and configurations were still available after the re-install and the system was working again.
To enable TRIM for a non Apple SSD device that was installed to my Macbook I am using Trim Enabler. The application disables a Kernel extension named kext-signing. This security setting prevents from installing 3rd party vendor firmware.
One week ago I had issues with high CPU usage and performed the NVRAM/PRAM reset. As described in the FAQ kext-signing needs to be enabled again before NV/PRAM reset.