Hi, maybe You also thinking if its really necessary to use two or more HDDs in Raid array to prevent data loss...

Raid PROs:
- Raid1, Raid 10 means no interuption in computer function if one drive in Raid fails...
- Possible higher reading or writing operation speed in case you have 3 or more drives in Raid (we dont talk about Raid0 as it increase chance of data loss)

Raid CONs:
- need to buy one more drive
- higher electricity bill
- slightly difficult setup

Alternatives to Raid is to do some kind of backup:
- full hdd backup if not incremental is probably too intensive and obstructive task
- backup only important data folders like My Documents, Program Files, Users/myUsername
A) backup locally to another drive on same PC (not too safe) or backup to removable USB drive (too difficult & boring to handle manually)
B) backup automatically to some remote server bought for this purpose (ie: http://www.kimsufi.com/us/en/ has 2Tb for around $35/mo.)
C) use specialised backup services which are mentioned on this page, example BackBlaze.
Im now using BackBlaze, it offers unlimited disk space and does backups automatically on background for $5 monthly. Read my tutorial about BackBlaze