The document provides a comprehensive overview of RAID (Redundant Array of Independent Disks), detailing its importance, concepts, implementation methods, performance issues, and comparisons among various RAID levels. RAID enhances data reliability and performance through techniques such as mirroring and striping, and discusses standard levels (0 to 6) and nested RAID configurations. It concludes with references and notes on the increasing integration of RAID technology in both enterprise and desktop computing.

2. Performance Evolution of
RAID
PresentationTopic

3. Member:
• Zubair Hossain (13103037)
Group: Processor

4. 1. What is RAID?
2. Importance of RAID
3. Concept about RAID
5. Standard Raid Level
6. Nested Raid Level
7. Implementation of Raid
8. RAID Performance Issue
9. Performance and Advantages Comparison
among RAID Levels
10.Conclusion
11.References
Index

5. WHAT IS RAID?
RAID MEANS REDUNDANT ARRAY OF INDEPENDENT DISKS.
IT IS ALSO CALLED REDUNDANT ARRAY OF INEXPENSIVE DISKS.

6. IMPORTANCE OF RAID
1. RELIABILITY
2. REAL-TIME DATA RECOVERY WITH UNINTERRUPTED ACCESS WHEN A HARD DRIVE FAILS
3. SYSTEM UPTIME AND NETWORK AVAILABILITY AND PROTECTION FROM LOSS PROTECTION
AGAINST DATA LOSS
4. MULTIPLE DRIVES WORKING TOGETHER INCREASE SYSTEM PERFORMANCE

7. CONCEPT ABOUT RAID
THE TWO FUNDAMENTAL RAID CONCEPTS :
Data
Redundancy
Data
striping

8. DATA REDUNDANCY
REDUNDANCY GIVES US THE ABILITY TO HAVE A DRIVE FAIL
WITHOUT LOSING VALUABLE DATA
There are Two Type of Data Redundancy
1. Disk Mirroring
2. Data Parity

9. DISK MIRRORING
• KEEP TO COPIES OF DATA ON TWO SEPARATE DISKS
• GIVES GOOD ERROR RECOVERY
• IF SOME DATA IS LOST, GET IT FROM THE OTHER SOURCE
• EXPENSIVE
• REQUIRES TWICE AS MANY DISKS
• WRITE PERFORMANCE CAN BE SLOW
• HAVE TO WRITE DATA TO TWO DIFFERENT SPOTS
• READ PERFORMANCE IS ENHANCED
• CAN READ DATA FROM FILE IN PARALLEL

10. DATA PARITY
• WAY TO DO ERROR CHECKING AND CORRECTION
• ADD UP ALL THE BITS THAT ARE 1
• IF EVEN NUMBER, SET PARITY BIT TO 0
• IF ODD NUMBER, SET PARITY BIT TO 1
• CONSIDER THE FOLLOWING 2 BYTES
BYTE PARITY
10110011 1
01101010 0
• IF A SINGLE BIT IS BAD, IT IS POSSIBLE TO CORRECT IT

11. DATA STRIPING
DATA STRIPING IS THE TECHNIQUE
OF SEGMENTING LOGICALLY
SEQUENTIAL DATA, SUCH AS A FILE,
SO THAT CONSECUTIVE SEGMENTS
ARE STORED ON DIFFERENT
PHYSICAL STORAGE DEVICES.

12. STANDARD RAID LEVEL
RAID – 0 (STRIPING)
RAID – 1(MIRRORING)
RAID – 2(Redundancy through Hamming code)
RAID – 3(Bit Interleaved Parity)
RAID – 4(Block Interleaved parity)
RAID – 5(STRIPING AND PARITY)
RAID-6 (P+Q redundancy)

13. RAID-0
DATA ARE STRIPPED ON ALL DISKS
OFFER PERFORMANCES
NO REDUNDANCY
2 DISKS MINIMUM, MAXIMUM DEPENDING OF RAID CONTROLLER
DATA ARE SPLIT DEPENDING OF STRIPE SIZE (16/32/64/128KB)
controller

14. RAID-1
DATA MIRRORED (DUPLICATED) ON SECOND HARD DISK
OFFER REDUNDANCY
EQUIVALENT OF ONE DISK SPACE LOST FOR REDUNDANCY
ONLY ON 2 DISKS
SUPPORT ONE DISK FAILURE
Controller

15. • STRIPES DATA AT THE BIT LEVEL
• USES A HAMMING CODE FOR ERROR CORRECTION.
• THE DISKS ARE SYNCHRONIZED BY THE CONTROLLER TO SPIN AT THE SAME
ANGULAR ORIENTATION
• EXTREMELY HIGH DATA TRANSFER RATES ARE POSSIBLE.
• THIS IS THE ONLY ORIGINAL LEVEL OF RAID THAT IS NOT CURRENTLY USED.
RAID-2

16. RAID-3
 RAID 3 IS CONFIGURED WITH AT LEAST THREE DRIVES
 TWO DRIVES CARRY THE DATA AND THE THIRD DRIVE CARRIES PARITY INFORMATION.
 USES BYTE-LEVEL STRIPING WITH A DEDICATED PARITY DISK.
 GENERALLY CANNOT SERVICE MULTIPLE REQUESTS SIMULTANEOUSLY.
 ANY I/O OPERATION REQUIRES ACTIVITY ON EVERY DISK AND USUALLY REQUIRES
SYNCHRONIZED SPINDLES

17. RAID-4
A RAID 4 USES BLOCK-LEVEL STRIPING WITH A DEDICATED
PARITY DISK.
OTHER ARE SAME AS RAID 3

18.  Stripes data and parity to generate redundancy.
 The parity is distributed through the stripe of the disk array.
 both parity and data are striped across a set of separate disks.
 Data chunks are much larger than the average I/O size, but are
still resizable.
 Disks are able to satisfy requests independently
RAID-5

19. RAID-6
 Data is striped across all disks (minimum of four)
 A two parity blocks for each data block (p and q in the
diagram) is written on the same stripe.
 If one physical disk fails, the data from the failed disk can be
rebuilt onto a replacement disk.
 Provides for faster rebuilding of data from a failed disk.

20. NESTED RAID LEVEL
LEVELS OF NESTED RAID, ALSO KNOWN AS HYBRID RAID COMBINE TWO
OR MORE OF THE STANDARD LEVELS OF RAID TO GAIN PERFORMANCE,
ADDITIONAL REDUNDANCY, OR BOTH.

21. Nested Raid Level
RAID-
(0+1) RAID-10 RAID-50 RAID-60

22. RAID (0+1)
• RAID-01 IS TECHNICALLY A
COMBINATION OF RAID-1 AND
RAID-0, INCLUDES BOTH
MIRRORING AND STRIPING, BUT
WITHOUT PARITY.

23. RAID 10
IT USES RAID-1MIRRORING AND RAID-0
STRIPING, AND HAS BOTH SECURITY AND
SEQUENTIAL PERFORMANCE.
IT IS A STRIPED RAID-0 ARRAY WHOSE
SEGMENTS ARE MIRRORED RAID-1.
IT IS SIMILAR IN PERFORMANCE TO RAID
0+1, BUT WITH BETTER FAULT TOLERANCE
AND REBUILD PERFORMANCE.
IT HAS THE SAME FAULT TOLERANCE AS
RAID-1 WITH THE SAME OVERHEAD FOR
FAULT TOLERANCE AS MIRRORING ALONE.

24. RAID-50
• COMBINES MULTIPLE RAID 5 SETS
WITH RAID 0 (STRIPING).
• REBUILD TIMES ARE
SUBSTANTIALLY LESS THAN A
SINGLE LARGE RAID 5 ARRAY.
• USABLE CAPACITY OF RAID 50 IS
BETWEEN 67% - 94%,
DEPENDING ON THE NUMBER OF
DATA DRIVES IN THE RAID SET.

25. RAID-60
• COMBINES MULTIPLE RAID 6 SETS WITH
RAID 0 (STRIPING).
• DUAL PARITY ALLOWS THE FAILURE OF
TWO DISKS IN EACH RAID 6 ARRAY.
• STRIPING HELPS TO INCREASE CAPACITY
AND PERFORMANCE WITHOUT ADDING
DISKS TO EACH RAID 6 ARRAY .

26. IMPLEMENTATION OF RAID
• THERE ARE TOW TYPES OF RAID IMPLEMENTATION.
Software
Implementation
Hardware
Implementation

27. SOFTWARE IMPLEMENTATION
• SOFTWARE RAID CAN BE IMPLEMENTED IN A VARIETY OF WAYS: IN THIS CASE,
THE RAID IMPLEMENTATION IS AN APPLICATION RUNNING ON THE HOST
WITHOUT ANY ADDITIONAL HARDWARE. THIS TYPE OF SOFTWARE RAID USES
HARD DISK DRIVES WHICH ARE ATTACHED TO THE COMPUTER SYSTEM VIA A
BUILT-IN I/O INTERFACE OR A PROCESSOR-LESS HOST BUS ADAPTER (HBA). THE
RAID BECOMES ACTIVE AS SOON AS THE OPERATING SYSTEM HAS LOADED
THE RAID DRIVER SOFTWARE.

28. SOFTWARE IMPLEMENTATION
SOFTWARE BASED RAID:
• SOFTWARE IMPLEMENTATIONS ARE PROVIDED BY MANY OPERATING SYSTEMS.
• A SOFTWARE LAYER SITS ABOVE THE DISK DEVICE DRIVERS AND PROVIDES AN
ABSTRACTION LAYER BETWEEN THE LOGICAL DRIVES(RAIDS) AND PHYSICAL
DRIVES.
• SERVER'S PROCESSOR IS USED TO RUN THE RAID SOFTWARE.
• USED FOR SIMPLER CONFIGURATIONS LIKE RAID0 AND RAID1.

29. HARDWARE IMPLEMENTATION
• A HARDWARE RAID SOLUTION HAS ITS
OWN PROCESSOR AND MEMORY TO
RUN THE RAID APPLICATION. IN THIS
IMPLEMENTATION, THE RAID SYSTEM IS
AN INDEPENDENT SMALL COMPUTER
SYSTEM DEDICATED TO THE RAID
APPLICATION, OFFLOADING THIS TASK
FROM THE HOST SYSTEM. HARDWARE
RAID CAN BE FOUND AS AN INTEGRAL
PART OF THE SOLUTION

30. HARDWARE IMPLEMENTATION
HARDWARE BASED RAID:
• A HARDWARE IMPLEMENTATION OF RAID REQUIRES AT LEAST A SPECIAL-
PURPOSE RAID CONTROLLER.
• ON A DESKTOP SYSTEM THIS MAY BE BUILT INTO THE MOTHERBOARD.
• PROCESSOR IS NOT USED FOR RAID CALCULATIONS AS A SEPARATE CONTROLLER
PRESENT.

31. • The key to performance increases under RAID is parallelism. The ability to
access multiple disks simultaneously allows for data to be written to or read
from a RAID array faster than would be possible with a single drive.
Performance Issue can be discussed by four points:
• Read and Write Performance
• Positioning and Transfer Performance
• Stripe Width and Stripe Size
RAID Performance Issue

32. • Mirroring: In Raid every piece of data is duplicated, stored on both drives. There's
absolutely no reason to access both drives; the controller, if intelligently programmed, will
only ask one of the drives for the data--the other drive can be used to satisfy a different
request. This makes RAID significantly faster than a single drive for reads, under most
conditions.
• Striping Without Parity: A RAID 0 array has about equal read and write performance . The
reason is that the "chopping up" of the data without parity calculation means we must
access the same number of drives for reads as we do for writes.
• Striping With Parity: As with mirroring, write performance when striping with parity (RAID
levels 3 through 6) is worse than read performance, but unlike mirroring, the "hit" taken
on a write when doing striping with parity is much more significant.
Read and Write Performance

33. • Mirroring: Mirroring improves positioning performance. However, once the
data is found, it will be read off one drive.
• Striping: Large files that are split into enough blocks to span every drive in
the array require each drive to position to a particular spot, so positioning
performance is not improved; once the heads are all in place however, data
is read from all the drives at once, greatly improving transfer performance.
On reads, small files that don't require reading from all the disks in the
array can allow a smart controller to actually run two or more accesses in
parallel. This improves both positioning and transfer performance.
Positioning and Transfer
Performance

34. • Decreasing Stripe Size: As stripe size is decreased, files are
broken into smaller and smaller pieces. This increases the number
of drives that an average file will use to hold all the blocks
containing the data of that file, theoretically increasing transfer
performance, but decreasing positioning performance.
• Increasing Stripe Size: Increasing the stripe size of the array does
the opposite of decreasing it, of course. Fewer drives are
required to store files of a given size, so transfer performance
decreases. However, if the controller is optimized to allow it, the
requirement for fewer drives allows the drives not needed for a
particular access to be used for another one, improving
positioning performance.
Stripe Size

35. Performance and Advantages
Comparison among RAID
Levels

37. RAID has been with us for about 20 years, but until only recently
it was the domain of big systems and deep pockets. During those
20 years, however, a number of factors have come together to
make RAID a reality for both big servers and common desktop
systems. Imagine a world where dirt-cheap RAID on every
computer means no one ever again losing critical data.
The first desktop RAID systems have already appeared on the
market. As disk size and cost continue to decline, widespread
use of RAID on the desktop is only a matter of time.
Conclusion

38. • 1. RAID for Enterprise Computing – Copyright @ VERITAS Software Corporation, 1999,
2000
• 2. RAID: High-Performance, Reliable Secondary Storage-
• 3. http://en.wikipedia.org/wiki/RAID
• 4. http://en.wikipedia.org/wiki/Non-
standard_RAID_levels#RAID_5E.2C_RAID_5EE.2C_and_RAID_6E
• 5. http://en.wikipedia.org/wiki/Standard_RAID_levels
• 6. http://en.wikipedia.org/wiki/Nested_RAID_levels
• 7. http://www.pcguide.com/
• 8. RAID Levels and Components Explained-Developed in Nov. 2007 by Jerry Scott
• 9. RAID Storage — Speed and Security (PDF)
• 10. RAID Theory: An Overview - Ben Rockwood, Cuddletech
• 11. Storage solutions white paper - Copyright 2006 Adaptec, Inc.
References