Back in February 2016, a pioneering project published in MacFormat magazine (pp 64-67) demonstrated how users could make their own ‘fusion drives’ by coupling a relatively inexpensive SSD with a hard drive, and using the
diskutil command to create a CoreStorage Logical Volume Group (LVG). Although I write for MacFormat, I can claim no credit for that article, which was painstakingly put together by Alan Stonebridge.
Many of these home-brew ‘fusion drives’ have worked very successfully ever since, but now that macOS Sierra is being installed by more and more users, I have heard of one which had been fine as a startup drive under El Capitan, but now refuses to install Sierra. This particular reader had a small glitch when setting up the LVG, but it has behaved normally since.
It’s hard to know whether this is a problem with his particular setup, or is more general to such home-brew LVGs; it clearly doesn’t affect Apple’s Fusion Drives, though.
This reader reports that the Sierra Installer app runs fine in its first phase, but when his Mac restarts to proceed with installing Sierra, it bounces straight back into El Capitan.
I’d be very interested to know of anyone else running a home-brew ‘fusion drive’ like this who has tried installing Sierra, and whether it worked OK, or they had similar problems, please. For the moment I am putting it on the list of bugs in Sierra, as a possibility. Hopefully others will be able to confirm whether it is more general.