Raid 1

Well since hard drives can fail for numerous reasons, just because one fails does not necessarily mean the other is close to failure. I have had hard drives last less than a year and some that are over 10 years old.

Anyways the main purpose of RAID 1 is that if one of your hard drives fails you can keep working as usual when the drive fails and install a replacement for the failed drive and rebuild the mirrored array, rather than spending hours rebuilding your computer from backups and software installers. The other point of RAID 1 is to have an exact mirror of another hard drive so that you are always protected from failure whereas even daily backups can not provide that level of protection.

Though there are benefits of RAID 1 that does not mean to not make backups. You are not protected from accidental file deletion in any array. There is no protection if you accidentally screw up your operating system. No matter how good the RAID array is it does not protect against fire, natural disaster or theft. For protection from these problems you need a backup solution that can be secured in at least a safe if not off location.