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 will
appear to the computer as a single logical storage unit or drive.
RAID is a method in which information is spread across several disks,
using 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 increase bandwidth for reading or writing
to disks, and 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 RAID according to the RAID level used. When the data is to
be read, the process is reversed, giving the illusion that multiple drives
are actually one large drive.
