I'd vote for the second option as it provides some extra flexibility -
e.g. you could run Firefly in parallel using only two processes
(rather that four) while allowing each process to have more scratch
space. However, perhaps some extra experimentation is needed to find
the best solution.
Another point to check is whether the SATA-II controller on your
system allows two separate SSDs to transfer data at the full speed
at the same time. If it does not, you'll need additional PCIe
>1. Make 2 separate filesystems on each SSD, so each process will have its files in the separate filesystem (I suppose this will be the best choice).
>2. Just make 2 directories on each SSD.
>3. Make RAID of these 2SSDs and create the only filesystem with 4 directories.