Using 2011 Macbook Pro in target disk mode to update from El Capitan to Sierra
FIRST SOME BACKGROUND
My 2011 Macbook Pro (El Capitan) has recently developed problems, e.g. fuzzy artefacts onscreen, black solid line dividing screen, fine horizontal blue lines on startup screen, difficult/unreliable to boot into normal or safe mode. When I ran the Macbook Pro in target disk mode attached to a 2016 MB Air (Sierra) I could reliable boot into the MB Pro from the MB Air without experiencing any of the artefacts on the MB Air described above for the MB Pro. I suspected discrete GPU/logic board issue which is common for this model - aka earlier Apple GPU/logic board replacement program.
Subsequently Genius Bar ran MRI diagnostics & VSt - all passed and they also attached an external monitor via thunderbolt to MB Pro while it was displaying graphic issues which did not replicate the graphics issues on the MB Pro. Genius suggested likely software issue and as 1st step to troubleshooting should update MAC OS from El Capitan to Sierra. (I'm not persuaded it is software related but lets park that thought for the moment.)
ACTION TO UPDATE FROM EL CAPITAN TO SIERRA
When I was able to boot the MB Pro into normal mode I downloaded the Sierra installer from the App Store & it auto opened on the screen and I continued to click thru the screens until the installation commenced. When the installer progress bar got to 100% the installer seemed to reboot the system (as expected) but unfortunately the reboot hung (not surprising given the earlier symptoms described above).
After multiple attempts to hard boot the system it finally booted into normal mode with the original system and apps preserved (ie El Capitan).
So my dilemma is that the very unreliability of the system to boot is causing a major impediment to successfully carrying out the Genius Bar instructions to update to Sierra.
Are there any suggestions of how I can update the MB Pro to Sierra in an environment where the unreliability of the MB Pro to reboot will interfere with the completion of the installation process?
My only thoughts would be to use target disk mode on the MB Pro (using thunderbolt cable) and run the installer from the MB Air to update the volume on the MB Pro to Sierra. Would this work? However doesn't part of the Sierra installer process use the MB Air wireless to briefly connect to the internet to get specific information about the Mac Model (in this case the MB Air and not the MB Pro) such as firmware updates?
Interested in your thoughts on a resolution.
MacBook Pro 15", OS X 10.11
