RAIDRedundant Arrays Of

Independent Disks

Group : 3

Miss Munni Unmul Habbiba (dc2013MCA00)Keyilamswabe (dc2013MCA00) Bikash dhal (dc2013MCA0028)

Introduction :

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.

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

Figure : RAID Level 0 (Striping)

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

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.

Figure : RAID Level 1 (Mirroring)

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.

Figure : RAID Level 2

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.

AdvantagesGood read and write performance

Disadvantages:High overhead for check disksNot used in modern systems

RAID Level 3

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.

Figure : RAID Level 4

RAID Level 4

Uses Block-level striping with dedicated parityRequires minimum of 3 drives to implementEach disk operates independently which allows I/O requests to

be performed in parallel.

AdvantagesRead Performance is very good because of the blocks.Lowest overhead of check disks.

DisadvantagesQuite complex controller designNot commonly used

Figure : RAID Level 5

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.

Figure : RAID Level 6

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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