As a bonus question, I'd like to know if he would benefit from having multiple SATA disks on RAID or a single SATA would be better off (regarding the writing performance of HDDs).
If loss of data is a concern, you definitely don't want to use the type of RAID array where several disks are treated as one-I can never remember if it's RAID 0 or 1. More disks that can fail, and if one goes then there goes your data.