The 10% cached LUN size, is that using RAM or using SSD?

I am trying to find out how much Cache I need, RAM and SSD. I am running StarWind in HA with 1tb. Current setup: Node 1 has 8gb RAM (max it can have is 32GB) Node 2 has 8gb RAM (max it can have is 16gb) I have not purchased any SSD's yet, but I am looking at the MLC SSD. Let me know if you need more...

I am wondering if I can setup an HA cluster with one node using SATA drives and the other using SAS?
If it won't work for performance reasons I could have the clients only access the SAS node correct?