The basic idea behind RAID is to combine multiple small, inexpensive disk
drives into an array to accomplish performance or redundancy goals not
attainable with one large and expensive drive. This array of drives
appears to the computer as a single logical storage unit or drive.
RAID is a method in which information is spread across several
disks. RAID uses techniques such as disk striping
(RAID Level 0), disk mirroring (RAID level 1),
and disk striping with parity (RAID Level 5) to
achieve redundancy, lower latency and/or to increase bandwidth for
reading or writing to disks, and to maximize the ability to recover from
hard disk crashes.
The underlying concept of RAID is that data may be distributed across
each drive in the array in a consistent manner. To do this, the data
must first be broken into consistently-sized
chunks (often 32K or 64K in size, although
different sizes can be used). Each chunk is then written to a hard drive
in the RAID array according to the RAID level used. When the data is to
be read, the process is reversed, giving the illusion that the multiple
drives in the array are actually one large drive.