RAID LEVELS

RAID LEVELS
UZAIR KHAN
MUHAMMAD SHAHAB

Contents:
 Introduction
 Abstract
 Major concepts
 Raid Levels
 Conclusion
 Reference

Introduction:
 RAID stands for Redundant Array of Independent Disks
or Redundant Array of Inexpensive Disks.
 RAID is an example of storage virtualization and was first
defined by David Patterson in 1987.
 RAID is a storage technology that combines multiple disk
drive components into a logical unit

Abstract:
 Storage scheme using multiple hard drives to share or
replicate data among the drives.
 It provide data integrity, fault-tolerance, throughput or
capacity compared to single drives.
 Instead of seeing several different hard drives, the OS sees
only one.
 Typically used on server computers, advanced personal
computers.

Major concepts that you should know!
 What is RAID?
 Why RAID?
 How does RAID work?
 Are there any alternatives to RAID?

What is RAID?
 Redundant Array of Inexpensive Disks.
Basic idea is to connect multiple disks together to provide
 Large storage capacity
 Faster access to reading data
 Redundant data

Why RAID?
 RAID system provides data redundancy, fault tolerance,
increased capacity and increased performance.
 RAID has for a long time been something that you only find
in large server systems, but lately cheaper RAID controller
card have made it possible to get a RAID system even for
small servers and home computers.

How does RAID works?
 Take some inexpensive disks and group them together, which
will make the system see them as one single disk.
 This is done by using a RAID controller card that handle all I/O
to the disks, and which knows where the stored data can be
found.

RAID controller:
 A RAID controller is a hardware device or software
program used to manage hard disk drives (HDDs) or
solid-state drives (SSDs) in a computer or
storage array so they work as a logical unit.

Are there any alternatives to RAID?
At the Berkeley University of California they perform
researches about alternative solutions.
 Such a solution is RADD, or Redundant Array of Distributed
Disks. RADD: can support redundant copies of data across a
computer network at the same space cost as RAID: do for
local data.
 Such copies increase availability in the presence of both
temporary and permanent failures (disasters) of single site
computer systems as well as disk failures.

RAID LEVELS:
 RAID 0 – striping
 RAID 1 – mirroring
 RAID 2 – redundancy through Hamming
 RAID 3 – bit interleaved Parity
 RAID 4 – block interleaved Parity
 RAID 5 – striping with parity

LEVEL 0 (striping):
 Striping means that each file is split into blocks of a certain
size and those are distributed to the various drives.
 Offers superior I/O performance.
 Performance can be enhanced further by using multiple
controllers.

Ideal use:
Photoshop image retouching station.
Advantages:
 Offers great performance.
 There is no overhead caused by parity controls.
 Easy to implement.
Disadvantages:
 Not fault-tolerant.
 It should not be used on mission-critical systems

LEVEL 1 (mirroring):
 Mirroring means duplication of data i.e
 Data are stored twice.
 Writing them to both the data disk and a mirror disk .
 The controller uses either the data drive or the mirror drive for
data recovery.

Ideal use:
Accounting systems.
Advantages:
Data do not have to be rebuild.
Disadvantages:
Storage capacity is only half of the total disk capacity .

LEVEL 2 (redundancy through Hamming):
 Bit-level striping means that the file is broken into “bit-sized
pieces”.
 It uses a Hamming code for error correction.

Ideal use:
 No commercial use.
Advantages:
 Data transferred rate is very high.
 Single bit errors can be detected and corrected.
 Multiple bit errors can be detected.
Disadvantages:
 Multiple bits error cannot be corrected.
 Raid 3 gives better performance at lower price.

LEVEL 3 (bit interleaved Parity):
 Byte-level striping means that the file is broken into "byte-
sized pieces“.
 Written in parallel on two or more drives.
 An additional drive stores parity information.

Ideal use:
 Video streaming.
Advantages:
 It provides high throughput for large data transfers.
 Disk failures do not significantly slow down
throughput.
Disadvantages:
 Performance is slower for random, small I/O
operations.

LEVEL 4 (block interleaved Parity):
 Block-level striping means that each file is split into blocks of
a certain size .
 Allows each member to act independently when only a single
block is requested.
 Service multiple read requests simultaneously.

Ideal use:
Enterprise level company to use it is Net App.
Advantages:
 Reading operations are very fast.
 Fault tolerance is very high.
Disadvantages:
 In degraded mode, its reading operation becomes slow.
 Writing operation on disks is extremely slow.

LEVEL 5 (striping with parity):
 Most common secure RAID level.
 Except that data are transferred to disks by independent read
and write operations.
 Instead of a dedicated parity disk, parity information is spread
across all the drives.

Ideal use:
 Application servers.
Advantages:
 Read data transactions are very fast while write data
are somewhat slow.
Disadvantages:
 Disk failures have an effect on throughput.
 This is complex technology.

Conclusion:
 Overall it provides systems with a variety of benefits
depending upon the version implemented.
 Most users will likely opt to use the RAID 0 for increased
performance without the loss of storage space.
 This is primarily because redundancy is not an issue for the
average user.

References:
 Jimmy Person (pt98jpr)
Gustav Everson (pt99gev)
Blekinge Institute of Technology, Sweden
 Garth Gibson, Randy H.Katz
David A. Paterson, Martin schulze
University of California
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RAID LEVELS

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