I have a late 2012 iMac with a spinning HD. I've been booting from an external SSD in a USB3 / UASP enclosure and keep infrequently-accessed files on the HD. For various reasons, I'd like to wipe the SSD and fuse the SSD and internal HD into a DIY Fusion Drive. Does anyone know if Fusion / CoreStorage is capable of working with this setup? I'm not sure if the system would know the external drive is an SSD and route files there accordingly. When I look in system profile, OS X is unaware that the external enclosure contains an SSD (and SMART / TRIM do not work over USB3).