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Serial ATA BIOS Setting Utility Introduction
RAID Levels
RAID (Redundant Array of Independent Disks) is a method of combining two hard disk drives into one
logical unit. The advantage of an Array is to provide better performance or data fault tolerance. Fault
tolerance is achieved through data redundant operation, where if one drives fails, a mirrored copy of the
data can be found on another drive. This can prevent data loss if the operating system fails or hangs.
The individual disk drives in an array are called members. The configuration information of each
member is recorded in the reserved sector that identifies the drive as a member. All disk members in
a formed disk array are recognized as a single physical drive to the operating system.
Hard disk drives can be combined together through a few different methods. The different methods are
referred to as different RAID levels. Different RAID levels represent different performance levels,
security levels and implementation costs. The RAID levels which the nVIDIA nForce3 250 chipset
supports are RAID 0, RAID 1, and JBOD.
RAID 0 (Striping)
RAID 0 reads and writes sectors of data interleaved between multiple drives. If any disk member fails,
it affects the entire array. The disk array data capacity is equal to the number of drive members times
the capacity of the smallest member. The striping block size can be set from 4KB to 128KB. RAID 0
does not support fault tolerance.
RAID 1 (Mirroring)
RAID 1 writes duplicate data onto a pair of drives and reads both sets of data in parallel. If one of the
mirrored drives suffers a mechanical failure or does not respond, the remaining drive will continue to
function. Due to redundancy, the drive capacity of the array is the capacity of the smallest drive.
Under a RAID 1 setup, an extra drive called the spare drive can be attached. Such a drive will be
activated to replace a failed drive that is part of a mirrored array. Due to the fault tolerance, if any RAID
1 drive fails, data access will not be affected as long as there are other working drives in the array.
JBOD (Spanning)
A spanning disk array is equal to the sum of the all drives when the drives used are having different
capacities. Spanning stores data onto a drive until it is full, then proceeds to store files onto the next
drive in the array. When any disk member fails, the failure affects the entire array. JBOD is not really
a RAID and does not support fault tolerance.