RAID 1 (mirroring) makes both drive 100% identical. This is not a backup, so you still need to make backups. RAID1 ensures that if one drive fails/dies, the computer can remain running on the other drive. When the bad drive is replaced, RAID1 will automatically duplicate the contents of the good drive to the new drive. As long as you replace the bad drive before the other drive fails, you are safe.
RAID1 will not protect you against viruses or malware. It also won't protect you from accidental file deletion, thus the need for backups.