RAID is an acronym for Redundant Array of Independent Drives. There are several different levels of RAID devices. The key is that if one of the drives fails, the information from that device is retained in the remaining drives. The different RAID levels range from storing all information in two separate locations, to using software gymnastics to share information on all drives so that any single drive failure will not allow any loss of data.
RAID (Redundant Array of Independent Disks) protects recorded video by storing it across multiple hard drives. It improves data reliability and read/write performance