This document presents information on RAID level 4 storage. It begins with introductions to RAID in general and RAID level 4 specifically. RAID level 4 improves performance through striping data across disks in blocks while providing fault tolerance with a dedicated parity disk. It allows recovery from any single disk failure. Reads can be overlapped for high performance, but writes require updating parity data, slowing small random writes. Applications include video/image editing and servers. In conclusion, RAID offers cost-effective high performance and redundancy for data storage.

1. YOBE STATE UNIVERSITY DAMATURU
FACULTY OF SCIENCE
DEPARTMENT OF COMPUTER SCIENCE
Damaturu, Nigeria.
E-mail:bmusa057@gmail.com
GROUP-4
PRESENTATION
ON
CSC-4322 (OPERATING SYSTEM)
RAID level 4
BY
U/CS/12/057
U/CS/12/058
U/CS/12/059
U/CS/12/060

2. Contents
 Introduction to RAID in General
 Introduction to RAID level 4
 Pictorial View of the RAID level 4
 Pons and Cons
 Limitations
 Summary
 Conclusion
 References

3. RAID: is a technology that is used to increase the performance and/or reliability of
data storage.
Is a method of concatenating multiple drives into one logical storage unit.
o Originally stood for Redundant Arrays of Inexpensive Disks.
o The term “inexpensive” was too ambiguous and was assumed to be referring to cost which
was not true.
o The term “inexpensive” was actually referring to the slight performance hit required to
make the data storage reliable.
o RAID technology was originally developed in 1987 at the University of California at
Berkeley.
o The original intention of the development team was to reduce the cost of mass storage by
combining small, cheap drives to replace larger, expensive disks. The Berkeley engineers
also wanted to provide a level of protection by including redundant information to ensure
that a disk failure would not cause the loss of access to data.
Introduction to RAID

4. Goal of RAID
Improve performance and reliability by using an array of many
small disks as opposed to a few large expensive disks.

5. What RAID Provides
 Fault tolerance
i. It prevent disk drive failures.
ii. It enables real-time data recovery.
 High I/O performance
 Mass data capacity
 Configuration flexibility
 Lower protected storage costs
 Easy maintenance

6. RAID 4 system consists of four drives working in parallel. Therefore it allows multiple small I/O’s to
be done at once, Still use a single disk for parity.
Basic Levels of RAID are
RAID level 4
Parity is a redundancy
check that ensures full
protection of data without
maintaining a full set of
duplicate data.
In this technique, you just
make a mirror copy of disk
which you want to protect
and in this way you have
two copies of data.
Is a collection of strips in
aligned multiple disk .

7. RAID level 4
improves performance by striping data across many disks in blocks,
and provides fault tolerance through a dedicated parity disk. allows
read operations to be overlapped.

8. RAID Level 4
D0,0
D1,0
D2,0
D3,0
D0,1
D1,1
D2,1
D3,1
D0,2
D1,2
D2,2
D3,2
P0
P1
P2
P3
D0,0  D0,1  D0,2 = P0

9. • Stripes data at a block level across several drives, with parity
stored on one drive - block-interleaved parity
• Allows recovery from the failure of any of the disks
• Performance is very good for reads
• Writes require that parity data be updated each time. Slows small
random writes but large writes are fairly fast
RAID 4

10. How the Partition Disks are Concatenated together

11. Pros And Cons Of The RAID 4
Advantages
 Good data availability.
 High performance for read operations.
 Cost effective - only one extra disk is required for parity.
Disadvantages
 Poor write performance.
 Poor small, random I/O performance.
The main limitation of the RAID 4 is due to its expected poor performance,
therefore there is no commercial implementations of it.
Limitations

12. Applications
o Video Production and Editing
o Image Editing
o Applications Servers
o PC Workstations
o Internet/Web Servers
o Workgroup/File Savers

13. Summary
 Increasing performance gap between CPU and IO
 Data availability a priority
 RAID meets the IO challenge:
o Performance via parallelism
o Data Availability via redundancy
o Flexibility via multiple RAID levels, each offer unique
performance/availability/cost tradeoffs

14. Conclusion
RAIDS offer a cost effective option to meet the challenge of exponential
growth in the processor and memory speeds We believe the size reduction of
personal computer disks is a key to the success of disk array, RAID is an
effective mass storage scheme for improving speeds for streaming application
purposes and increasing redundancy to ensure data safety.

15.  C G Bell, “The Mm1 and Micro Industries,’ IEEE Computer Vol. 17 No 10 (October
1984). page 14-30
 K Salem and Garcia-Mohna, H , “Disk Striping,” IEEE 1986 International Conference
on Data Engineering, 1986
 http://www.bridgeport.edu/sed/fcourses/cpe473/Lectures/RAID.ppt
 http://www. r61505.csie.nctu.edu.tw/OG/project/extra6-Ch8RAID.ppt
 A. Silberschatz, P. B. Galvin, and G. Gagne, Operating System Concepts, 7th Edition,
John Wiley & Sons, 2005
References