An Introduction To Raid - Silicon Image SATA RAID FOR Manual

2 An Introduction to RAID

RAID - Redundant Array of Independent Disks
RAID technology manages multiple disk drives to enhance I/O performance and provide redundancy in order to withstand the
failure of any individual member, without the loss of data. There are many different methods of implementation for RAID, with
each having advantages and disadvantages. Raid levels or set types are given a numerical designator that defines its
implementation such as RAID 0 or RAID 1. SATARaid provides support for three RAID Set types: Striped (RAID 0) , Mirrored
(RAID 1), and RAID 10 Mirrored/Striped. Other RAID types are not supported by SATARaid software and thus are not
discussed.
Disk Striping (RAID 0)
Striping is a performance-oriented, non-redundant data mapping technique. While Striping is discussed as a RAID Set type, it
is does not provide any fault tolerance. With modern SATA and ATA bus mastering technology, multiple I/O operations can be
performed in parallel, enhancing data throughput. Striping arrays use multiple disks to form a larger virtual disk. The figure
below illustrates a three-disk stripe set. Stripe one is written to disk one, stripe two to disk two, and so forth. RAID 0 sets can
be comprised of two, three, or four drives.
Stripe0
Stripe3
Stripe6
Stripe9 Stripe10
Disk Mirroring (RAID 1)
Disk mirroring creates an identical twin for a selected disk by having the data simultaneously written to two disks. This
redundancy provides instantaneous protection from a single disk failure. If a read failure occurs on one drive, the system reads
the data from the other drive. RAID 1 sets are comprised of two drives. A third drive can be allocated as a spare in case one
of the drives in the set fails.
Block 0
Block 1
Block 2
Block 0
Block 3
Block 1
Block 2
Block 3
Disk Mirroring and Striping (RAID 10)
RAID 10 combines the features of both RAID 0 and RAID 1. Performance is provided through the use of Striping (RAID 0),
while adding the fault tolerance of Mirroring (RAID 1). The implementation of RAID 10 requires four drives. The drives are
assigned as two sets of striped pairs.
The data is written to RAID Set A, which is striped (RAID 0). This allows maximum speed. The data is then mirrored to another
RAID 0 striped set, which is Set B in the figure above. This provides data redundancy (RAID 1), and thus increased data
security.
Under certain circumstances, a RAID 10 set can sustain multiple simultaneous drive failures.
Copyright © 2003 Silicon Image Inc.
6
Stripe1 Stripe2
Stripe4 Stripe5
Stripe7 Stripe8
Stripe11
SATARaid User's Manual