RAID definition

RAID (Redundant Array of Independent Disks) is a method of configuring member drives to create high availability and high performance systems. The RAID level provides different degrees of redundancy and performance; it also determines the number of members in the array.

The RAID level determines the relationship of the disks.

Level	Description	Drive count	Approximate array capacity	Redundancy*
RAID 0	Combines two or more disks by striping data across them. Chunks of data are written to each disk in the array alternately.	1 - 8	Drive count × Drive size	None
RAID 1	A configuration that mirrors data between two or more disks. Everything written to the array is placed on each device in the group, so each disk has a complete set of the available data.	2	Drive size	1

*Redundancy indicates how many drive failures the array can tolerate. In some circumstances, an array can tolerate more than 1 drive failure.