Eccouncil Exam 312-38 Topic 7 Question 5 Discussion

Will is working as a Network Administrator. Management wants to maintain a backup of all the company data as soon as it starts operations. They decided to use a RAID backup storage technology for their data backup plan. To implement the RAID data backup storage, Will sets up a pair of RAID disks so that all the data written to one disk is copied automatically to the other disk as well. This maintains an additional copy of the data.Which RAID level is used here?