Introduction to

RAID Technology

Name: Maulik MangukiyaClass : TYBCADiv : 2Roll No : 78

History behind RAID

What is RAID?

RAID : Level 0 to Level 6 What that level means & does? Working with help of diagram

Benefits of using RAID Level

Content

History of RAID:

In 1987, Patterson, Gibson and Katz at the University of California at Berkeley, published a paper entitled “A Case for Redundant Arrays of Inexpensive( Independent ) Disks (RAID)”

I/O becoming a performance bottleneck

What is RAID? It is multiple-disk database design.

It is a category of disk drives (two or more) in combination for fault tolerance and performance.

It has seven levels – zero to six

RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.

RAID allows you to store the same data redundantly (in multiple places) in a balanced way to improve overall storage performance.

Different RAID Levels:

Different levels which provides a different balance between performance, capacity and tolerance.

Following are they:

LEVEL 0 : Striping

Minimum nos. of drives required : 2

Striping is the segmentation of logically sequential data, such as a single file, so that segments can be assigned to multiple physical devices

The first byte of the file is sent to the first drive, then the second to second drive and so on.

Diagram:

LEVEL 1: Mirroring and Duplexing

Minimum nos. of drives required : 2

RAID-1 provides data redundancy.

Data written to one disk drive is simultaneously written to another disk drive, called the mirroring.

Higher availability will be achieved if both disks in a mirror pair are on separate I/O busses, known as Duplexing.

Diagram:

LEVEL 2: Error-Correcting Coding

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.

LEVEL 3: Bit-Interleaved Parity

Minimum nos. of drives required : 3

A block of data is striped over an array of disks, then parity data is written to a dedicated parity disk.

Successful implementations usually require that all the disks have synchronized rotation.

RAID3 is very effective for large sequential data, such as satellite imagery and video.

Diagram:

LEVEL 4: Dedicated Parity Drive

Minimum nos. of drives required : 3

Level 4 provides block-level striping (like Level 0) with a parity disk.

If a data disk fails, the parity data is used to create a replacement disk.

Diagram:

LEVEL 5: Block Interleaved Distributed Parity

Minimum nos. of drives required : 3

It distributes parity along with the data and requires that all drives but one be present to operate. The array is not destroyed by a single drive failure.

On drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user.

Diagram:

LEVEL 6: Independent Data Disks with Double Parity

Minimum nos. of drives required : 2

RAID 6 provides fault tolerance up to two failed drives.

Raid Level 6 uses Block-level striping with dual distributed parity.

Diagram:

Benefits of RAID: Data loss can be very dangerous for an

organization

RAID technology prevents data loss due to disk failure

RAID technology can be implemented in hardware or software

Servers make use of RAID technology

Table: RAID Levels

Thank You