RAID is not a backup! It will help protect against disk hardware failure, but should not be considered a backup. When you accidentally delete your photos, the change is immediately mirrored to the other disk(s).
If on a Mac, use time machine or a third party program like Carbon Copy Cloner to an external or network attached disk. For Windows systems, I prefer options that don't require the original backup program to recover/restore files. Cobain backup (free) is one such option, or you could go really simple and use something like rsync or Robocopy. Recent versions of Windows have basic backup functionality built in.
For the ultimate protection, look at something that includes an offsite element. Crashplan can do both local and remote site backups.
Most critically, you need to regularly test your solution to make sure you can actually recover files!