RAID (Redundant Arrays of Independent Disks) uses multiple disk drives to increase performance and reliability. It distributes data across several disks that act as one large drive. There are different RAID levels that offer varying degrees of performance and fault tolerance. RAID levels 0 through 6 were described, with RAID 0 offering striping for performance but no redundancy, RAID 1 using mirroring for redundancy but no performance gain, and RAID levels 3 through 6 employing striping with varying parity techniques for performance and redundancy.

1. RAID
Redundant Arrays Of
Independent Disks
Group : 3
Miss Munni Unmul Habbiba (dc2013MCA00)
Keyilamswabe (dc2013MCA00)
Bikash dhal (dc2013MCA0028)

2. Introduction :

3. Solution: RAID
 Technology that employs the simultaneous use of two or more
hard disk drives to achieve greater levels of performance &
reliability.
 Several physical disks are set up to use RAID technology, they are said
to be in a RAID array.
 This array distributes data across several disks, but the array is seen by
the computer user and operating system as one single disk.

4. Different Levels of
RAID
 RAID Level 0
 RAID Level 1
 RAID Level 2
 RAID Level 3
 RAID Level 4
 RAID Level 5
 RAID Level 6

5. Figure : RAID Level 0 (Striping)

6. RAID Level 0
 Requires a minimum of 2 drives to implement.
 The first byte of the file is sent to the first drive, then the
second to second drive and so on.
 Striping is the segmentation of logically sequential data, such
as a single file, so that segments can be assigned to multiple
physical devices

7. RAID Level 0
 Advantages:
 I/o performance is greatly improved by spreading the i/o load
across many channels & drives.
 Best performance is achieved when data is striped across
multiple controllers with only one drive per controller.
 Disadvantages:
 It is not a “True” RAID because it is NOT fault-tolerant. The
failure of just one drive will result in all data in an array being
lost.

8. Figure : RAID Level 1 (Mirroring)

9. RAID Level 1
Data duplicated, also the controller card
Requires only two drives to implement
 Duplicate copies of data, so if a disk fails, data is still available
and applications keep running.
Advantages
Better than single disk
Simple to Implement
Disadvantage - high check disk overhead.

10. Figure : RAID Level 2

11. RAID Level 2
Uses Bit-level striping with Hamming codes of ECC.
Disks are synchronized and striped in very small stripes, often
in single bytes/words.
Hamming codes error correction is calculated across
corresponding bits on disks, and is stored on multiple parity
disks.
Advantages
Good read and write performance
Disadvantages:
High overhead for check disks
Not used in modern systems

12. RAID Level 3

13. RAID Level 3
Uses dedicated parity disk.
Requires a minimum of 3 drives to implement.
Every write requires updation in parity data .
Advantages
improved performance and fault tolerance.
Disadvantages:
 One minor benefit is the dedicated parity disk allows
the parity drive to fail and operation will continue
without parity or performance penalty.

14. Figure : RAID Level 4

15. RAID Level 4
Uses Block-level striping with dedicated parity
Requires minimum of 3 drives to implement
Each disk operates independently which allows I/O requests to
be performed in parallel.
Advantages
Read Performance is very good because of the blocks.
Lowest overhead of check disks.
Disadvantages
Quite complex controller design
Not commonly used

16. Figure : RAID Level 5

17. RAID Level 5
Uses Block-level striping with distributed parity
Requires a minimum of 3 drives to implement
Advantages
Read performance very good.
Lowest overhead of check disks.
Disadvantages
Most complex controller design.
Difficult to rebuild in the event of a disk failure.

18. Figure : RAID Level 6

19. RAID Level 6
 Raid Level 6 uses Block-level striping with dual distributed
parity.
Advantages:
Continues to operate with up to two failed drives.
Disadvantages
Most complex controller design.
Difficult to rebuild in the event of multiple disk failure.

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