I had intended investigating Raid 0, thinking it would give backup and more speed. (forgotten the source of that gem) However, I see a LOT of minus points in going that route, including loss of TRIM.
Two separate drives seems to be the answer, and right now I'm using the 2-1/2" drive from a defunct HP laptop as the on-board backup. The next backup level is a remote USB HD and memory sticks.
Both drive types are partitioned to give four logical drives. Any strong opinion about NOT partitioning SSDs?