I guess that wasn't clear. I was speaking about the single fusion drive as a hybrid SSD / HDD being one volume. You can't choose which files go on the SSD side of the fusion drive, like you said. NOT that I formatted two separate drives as some kind of JBOD. I wonder if that would even be possible...
I have a fusion drive in my mid 2010 mbp (after the original hdd went kaboom). It is meant primarily as an OS drive, as the OS seems to keep the startup files on ssd partition for extremely fast booting. (although not as fast as my girlfriend's 2012 macbook air with ssd) As Danny said, there's no way to control which data goes where on the disk. for the user it's seen as a single volume. However it has made my mac feel significantly faster and I consider it a great upgrade, for an OS drive in a laptop. Not so much as a cache / project drive though.
The OS determines whats on the SSD. its completely transparent to the user.
If you want to use an SSD for the AE cache there is no way to set unless you have a discreet SSD.
i work at a place where they put an SSD in an external TB case and have it mounted to the back of the imac and thunderbolt connected, so thats an option as well.
If you have an extra system that you want to see how it may work there apparently is a way from the terminal to make your HD and SSD one volume and OSX will manage it as a fusion drive. i have it tried it so ymmv...
I'm curious if anyone has played with the fusion drive set-up in a production environment on the new iMacs? We're debating on whether or not we want to spend the extra $1,000 on an SSD or not. I'd prefer to do it that way, but the budgeteers want to save the money... :)
I'm mostly wondering how well it'll work with an AE cache? And if you can determine what is installed on the SSD in the fusion drive setup. for instance, I have a ton of apps that I really don't care if they are on the SSD or not, I just want my pro apps on the SSD, and then use the remaining space for the AE cache.