As long as you are going to use the fourth drive by itself, you can use EITHER SAS or SATA, and it will need to be configured in a single-disk RAID 0.
Hi, I have a PE1950 with a 2.5" x 4 backplane and PERC 5i.  Currently it has 3 x 2.5" SAS drives on a RAID 5 configured single volume.  I want to add a large capacity 2.5" drive in the empty 4th slot and use it as a single-disk backup volume.  Must I purchase a SAS drive or can I use a SATA drive?  Also, if SATA is a possibility, which interposer and caddy will I need, if any? Many thanks!! -sul.
Adding an HD to PE1950. SAS or SATA?