RAID (redundant array of independent disks) is a data storage virtualization technology that combines multiple disk drives into a logical unit for the purposes of data redundancy or performance improvement.
Data is distributed across the drives in one of several ways, referred to as RAID levels. There are a number of different RAID Levels.
RAID 0 comprises striping. This level provides no data redundancy but improves performance through parallelism of read and write operations across multiple drives. RAID 0 has no error detection mechanism, so the failure of one disk causes the loss of all data on the array. Generally you could almost double the speed of read & write operations using RAID 0, but this has almost become obsolete with the introduction of SSD (Solid State Disk) drives which run at 3 or 4 times faster that the standard Hard Disk Drive.
RAID 1 comprises mirroring (without parity or striping). Data is written identically to two (or more) drives, thereby producing a "mirrored set". The array continues to operate as long as at least one drive is functioning.
The main benefit of RAID 1 is in case one of the hard drives has a physical failure. If one of the hard drives fails then the data on the 2nd hard drive should be preserved and can be used.
The problem with considering a RAID 1 as your backup is that it doesn’t eliminate accidental file deletion, corruption by applications or viruses.
So if you accidentally delete a file, it will instantly be removed from both mirrored copies, but you should have a Recycle Bin to recover the deleted files.
If your disk is corrupted by a virus or software problem, the corruption will effect both mirrored copies simultaneously.
The way around this is to have another external hard drive that you can copy all your files to in case any of the above may happen.