Raid level

RAID
Presented By:- Suveeksha Jain
College:- SJEC
Class:- Mtech 1 sem

CONTENTS
 Introduction
 Abstract
 Raid Levels
 Application
 Advantages of RAID
 Disadvantages of RAID
 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 server
sees only one.
 Typically used on server computers, advanced personal
computers.

The RAID controller combines several physical hard disks to
create a virtual hard disk. The server sees only a single virtual
hard disk. The controller hides the assignment of the virtual
hard disk to the individual physical hard disks.

RAID LEVELS
 Raid level 0
 Raid level 1
 Raid (0+1) or Raid 10
 Raid level 2
 Raid level 3
 Raid level 4
 Raid level 5

RAID 0 (BLOCK BY BLOCK STRIPING)
 Striping means that each file is split into blocks of
a certain size and those are distributed to the
various drives.
 Increases performance.

RAID 0 (striping): As in all RAID levels, the server sees only the
virtual hard disk. The RAID controller distributes the write
operations of the server amongst several physical hard disks.
Parallel writing means that the performance of the virtual hard
disk is higher than that of the individual physical hard disks.

Ideal use
Photoshop image retouching station.
Advantages
 Offers great performance.
 Easy to implement.
Disadvantages
 Not fault-tolerant.

RAID 1(BLOCK BY BLOCK 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.

RAID 1 (mirroring): As in all RAID levels, the server sees only the
virtual hard disk. The RAID controller duplicates each of the
server’s write operations onto two physical hard disks. After the
failure of one physical hard disk the data can still be read from the
other disk.

Ideal use
Accounting systems.
Advantages
 Data do not have to be rebuild.
 Primary importance for fault tolerance.
Disadvantages
 Storage capacity is only half of the total disk capacity .

RAID(0+1) OR RAID10
 It represents two stage virtualization.
 Raid(0+1) represents mirrored stripes.
• First level four hard disk to form two virtual hard
disk by means of striping, second level two virtual
hard disk into single virtual by mirroring.
 Raid10 represents striped mirrors.
• Vice versa to the above.

RAID 0+1 (mirrored stripes): As in all RAID levels, the server sees only
the virtual hard disk. Internally, the RAID controller realises the virtual
disk in two stages: in the first stage it brings together every four physical
hard disks into one virtual hard disk that is only visible within the RAID
controller by means of RAID 0 (striping); in the second stage it
consolidates these two virtual hard disks by means of RAID 1 (mirroring)
to form the hard disk that is visible to the server.

RAID 10 (striped mirrors): As in all RAID levels, the server sees only the
virtual hard disk. Here too, we proceed in two stages. The sequence of
striping and mirroring is reversed in relation to RAID 0+1. In the first stage
the controller links every two physical hard disks by means of RAID 1
(mirroring) to a virtual hard disk, which it unifies by means of RAID
0(striping) in the second stage to form the hard disk that is visible to the
server.

RAID 2 (BIT-LEVEL STRIPING WITH DEDICATED
HAMMING-CODE PARITY)
 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.

RAID 3(BYTE-LEVEL STRIPING WITH A DEDICATED PARITY
DISK)
 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.

RAID 4 (BLOCK-LEVEL STRIPING WITH A DEDICATED PARITY
DISK)
 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.

RAID 4 (parity disk) is designed to reduce the storage
requirement of RAID 0+1 and RAID 10. In the example, the data
blocks are distributed over four physical hard disks by means of
RAID 0 (striping). Instead of mirroring all data once again, only a
parity block is stored for each four blocks.

Ideal use
Enterprise level company to use it is NetApp.
Advantages
 Reading operations are very fast.
 Fault tolerance is very high.
Disadvantages
 Writing operation on disks is extremely slow.

RAID 5 (BLOCK-LEVEL STRIPING WITH PARITY DATA
DISTRIBUTED ACROSS ALL DISK )
 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.

RAID 5 (striped parity): In RAID 4 each write access by the
server is associated with a write operation to the parity disk for
the update of parity information. RAID 5 distributes the load of
the parity disk over all physical hard disks.

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.

APPLICATION
 Bank.
 Video streaming.
 Application Server.
 Photoshop image retouching station.

ADVANTAGES 0F RAID
 RAID allows form of backup of the data in the storage .
 Its is Hot Swappable.
 Ensures data reliability, increase in performance.
 Increase the parity check.
 Disk Stripping make multiple smaller disks look like one
large disk.

DISADVANTAGES
o It cannot completely protect your data.
o System should support RAID drives.
o Difficult to configure a RAID system.
o Costly, must purchase and maintain RAID controllers and
dedicated hard drives.
o It may slower the system performance.
o RAID is not data protection, but to increase access speed.

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.

REFERENCE
 www.google.com
 www.wikipedia.com
 http://www.raidrecoverysolutions.com/index.php?op
tion=com_content&view=article&id=22&Itemid=20
 http://www.pcguide.com/ref/hdd/perf/raid/levels/sing
leLevel2-c.html

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