There's various standard RAID levels from RAID 0 to RAID 6.

RAID 0: stripes the knowledge across a set of drives but in case you lose a drive you lose everything
RAID 1: mirrors the knowledge to another disk usually in mirrored pairs of
RAID 3: stripes the knowledge & has a drive for parity
RAID 4: distributes knowledge & parity across the drives in case you lose
RAID 6: distributes knowledge & doubles the parity allowing for a drive failure
The most often used configuration is RAID. In order to understand what RAID is you require to understand how the hard drives work in your computer or externally in an enclosure. In order to have a RAID configuration you will require a maximum of hard disks. For our purposes they are going to be using hard drives in our configuration.

The computer must have a RAID controller inside the computer on the motherboard in order to connect the hard drives. The other option is to have an outside RAID enclosure to hold the hard disks. With disks in the configuration each block of knowledge is being written & spread across those drives writing a marker (parity bit) in case there is a loss of of those drives. In the event of a drive failure the remaining drives carryover the load using the parity bit so it is not noticed by the finish user of the computer. The parity bit keeps track of errors as each block of knowledge is written to the hard drives. In the case of the loss of a second drive that would be catastrophic even for a RAID configuration to handle. Usually RAID devices have LEDs on the drive enclosures that glow red in case of drive failure. The RAID unit manufacturer ought to provide alerting program that will work together along along together with your operating technique & the technique log to notify you of a failure as well. times the failed drive is replaced the RAID unit will rebuild the knowledge on the new drive re-establishing the RAID set like new. Recovery from the drive failure & the later rebuild technique may take several hours & will degrade the performance of your computer until completed.

Raid on motherboard is available from a few manufacturers. While not common in desktop PCs there is options allowing you to put in outside RAID enclosure with minimal work.