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.
