It is not necessary for a RAID setup but is recommended for any server based setup for redundancy. Based on your title, are you planning on running a SSD with two SATA drives in RAID1 or running a SSD in RAID1 alone?
My question is I would like to use ssd as OS, so do I need to use 2 ssd as raid 1 for the OS ?
My data is on raid 5 with 3 x 1 Tb sata. I plan to use this setup for exchange server and application server.