It depends what you are doing. If you have a mostly read workload, then RAID 5 as you’ll have more spindles to read off of. If you have a mostly write workload, then RAID 1 as you don’t have any parity calculations to deal with. That said, if you put enough disks behind the RAID 5 that will mostly overcome the parity calculation performance hit and write performance will even out. Learn more: RAID Levels Explained.