Redundant array of inexpensive disks (RAID) is used to configure a disk subsystem to provide better performance and fault tolerance for an application. The basic idea behind using RAID is that you spread data across multiple disk drives so that I/Os are spread across these drives. RAID has special significance for database-related applications, where you want to spread random I/Os (data changes) and sequential I/Os (for the transaction log) across different disk subsystems to minimize disk head movement and maximize I/O performance.
The four significant levels of RAID implementation that are most common in database implementations are as follows:
RAID 0 is data striping with no redundancy or fault tolerance.
RAID 1 is mirroring, ...