Present of Raid and Its Type

COMPUTER
ARCHITECTURERAID AND ITS LEVELS

WHAT IS RAID
RAID Stands For: Redundant Array of Independent Disks
A Storage technology that combines multiple disks into
a single logical unit.

Motivation For RAID
Just as additional memory in form of cache , can improve system
performance , in the same way additional disks can also improve system
performance
In RAID , we use an array of disks . These disks operate independently
A Single I/O operation can be handled in parallel If data required is
distributed across multiple disks.

Benefits of RAID
 Data loss can be very dangerous for an organization. RAID tech
prevents data loss due to disk failure.
 RAID tech can be implemented in hardware or software.
 Servers make use of RAID technology

RAID Technology
There are seven levels o raid schemes. These
are called RAID 0,RAID 1,…. RAID 6
The common characteristics in this common
levels is:
 A set of physical disk drives.
 The Operating system views these separate disk as a
single local disk.
 Data is distributed across the physical drives o the
array.
 Redundant disk capacity is used to store parity
information.
 Parity information can help in recovering data in case of
disk failure

RAID level 0
 There is no parity checking of data.
 So if data in one drive gets corrupted then all the data
 Would be lost. Thus RAID 0 does not support data
recovery .
 Spanning is another term which is used in RAID level 0
because the logical disk will span all the physical
drives.
 RAID 0 implementation requires minimum 2 disks

Advantages
 RAID 0 offers great performance, both in read and
write operations.
 There is no overhead caused by parity controls.
 All storage capacity is used, there is no overhead.
 The technology is easy to implement

Disadvantages
 RAID 0 is not fault-tolerant.
 If one drive fails, all data in
the RAID 0 array are lost.
 It should not be used for
mission-critical systems

RAID level 1
 DATA stripping is used as in RAID 0, but each
logical strip is mapped to two separate
physical drives.
 Thus every disk in the array has a mirror disk
that contains a same data
 Data can be read from either disk but is
written on both disk

Advantages
 RAID 1 offers excellent read speed and a
write-speed that is comparable to that of a
single drive.
 In case a drive fails, data do not have to be
rebuild, they just have to be copied to the
replacement drive.
 RAID 1 is a very simple technology.

Disadvantages
 The main disadvantage is that the effective
storage capacity is only half of the total drive
capacity because all data get written twice.
 Software RAID 1 solutions do not always
allow a hot swap of a failed drive.
 Such systems typically use hardware
controllers that do support hot swapping

RAID level 2
 RAID 2 system provides protection in case
hard drives in the subsystem incur problems
or otherwise fail..

Advantages
 This level builds fault tolerance based on
Hamming Error Correction Code (ECC),
which is used to maintain the integrity of
data.
 Consequently, the higher rate of data
transfer required, the better the ratio of
data disks to ECC disks.
 Relatively, the controller design is simpler
than that of RAID levels 3,4 & 5.

Disadvantages
 Commercially is unviable as it is inefficient,
transaction data rate is at the rate of a single
disk at best (with spindle synchronization).
 Entry level cost very high - requires very high
transfer data rate requirement to justify very
high ratio of ECC disks to data disks.

RAID level 3
 RAID 3 is a Redundant Array of Independent
Disks (RAID) standard that uses striping at
the byte level and stores dedicated parity bits
on a separate disk drive. RAID 3 requires a
special controller that allows for the
synchronized spinning of all disks.

Advantages
 High throughput for transferring large
amounts of data.
 Resistant to disk failure and breakdown,
which leads to RAID 3's main
disadvantages (below).

Disadvantages
 The configuration may be too much if a
small file transfer is the only requirement.
 Disk failures may significantly decrease
throughput.

RAID level 4
 RAID 4 is a Redundant Array of Independent
Disks (RAID) standard configuration that uses
block-level data striping and a dedicated disk
for storing parity bits.
 It does not require synchronized spinning,
and each disk functions independently when
single data blocks are requested.

Advantages
 Data block striping, which facilitates
simultaneous I/O requests.
 Low storage overhead, which lowers as
more disks are added.
 Does not require synchronized spindles or
controller.

Disadvantages
 Parity drives may lead to bottlenecks
 Slow random writes, which result when a
parity must be separately written for each
write.

RAID level 5
 RAID 5 is a standard RAID level configuration
that uses block-level data striping and
distributes parity to all the disks.
 There is still some overhead during parity
calculations, but since parity is written to all
disks, no single drive can be considered the
bottleneck, and I/O operations are spread
evenly across all drives.

Advantages
 Can tolerate the loss of a single drive.
 Good random read performance.
 Good sequential read and write
performance.

Disadvantages
 Parity calculation may slow down system
 Due to parity overhead, random write
performance takes a hit.

RAID level 6
 RAID 6 is a type of RAID level that utilizes
block-level striping and distributes two parity
blocks on each disk within the array.
 It is considered an enhancement to RAID
level 5, but adds an additional parity block on
each disk in the array.
 RAID 6 is also known as double-parity RAID.

Present of Raid and Its Type

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