RAID (Redundant Array of Independent Disks) combines multiple disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both. There are several common RAID levels. RAID levels 0 and 1 are for performance and mirroring respectively, while RAID levels 3, 4, 5, and 6 provide redundancy through parity-based schemes, with levels 5 and 6 capable of recovering data if two drives fail simultaneously. The document provides details on the characteristics, advantages, and disadvantages of various RAID levels.

1. COMPUTER
ARCHITECTURERAID AND ITS LEVELS

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

3. 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.

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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.

11. 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

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

13. 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.

14. 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.

15. 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.

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

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

18. 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.

19. 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.

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

21. 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.

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

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

24. 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.