RAID: High-Performance, Reliable Secondary Storage

Mei Qing & Chaoxia Liao

Nov. 20, 2003

Outline

PART I: Basic RAID Introduction RAID organization

PART II: Performance Improvement Performance Analyze RAID 5 Improvement

Conclusion Limitation Future Work

PART I Basic RAID

Introduction

BackgroundWhat is RAID

RAID stands for Redundant Array of Inexpensive Disks

Driving force of RAIDFaster MicroprocessorsDramatic increase in the amount of data

needed to serve and storeStorage technologies is very expensive

Intruduction

Advantage of RAIDRedundancy

MirrorParity distribution

Increased Performance Striping

Lower Costs

Basic RAID Organization

RAID levels 0 to 5RAID 0 (Non-redundant)RAID 1 (Mirrored)RAID 2 (Memory-Style ECC)RAID 3 (Bit-Interleaved Parity)RAID 4 (Block-Interleaved Parity)RAID 5 (Block-Interleaved Distributed-

parity)

RAID Level 0

Advantage & Disadvantage Good performance on read Low cost No redundancy Simple Design Easy to implement

Recommended Applications Video Production and

Editing Image Editing Any application requiring

high bandwidth

RAID Level 1

Advantage & Disadvantage Fast on Read Slow on Write Very good redundancy High Cost

Recommended Applications Accounting Payroll Financial Any application requiring

very high availability

RAID Level 2

Hamming Error Correction Code

RAID Level 3

Advantage and Disadvantage High efficiency Good read and write Data access in parallel

Recommended Applications Video Production and live

streaming Image Editing Video Editing Prepress Applications Any application requiring

high throughput

RAID Level 4

RAID Level 5

Advantage & Disadvantage Best small read, large read

and large write performance Overcome the bottleneck of

the parity Good reliability Inefficiency small write

because of the overhead of distributed parity

Recommended Applications File and Application

servers Database servers WWW, E-mail, and News

servers Intranet servers Most versatile RAID level

Further Develop on RAID

Multiple Nested RAIDRAID level 1+0RAID level 0+1RAID level 53RAID level 0+5

RAID Level 1+0

Advantage & Disadvantage Good fault tolerance Good rebuilt performance Good read and write

performance Not require parity calculation

Recommended Applications Database server requiring

high performance and fault tolerance

RAID Level 53

RAID Implement Hardware RAID

More efficiency Operating system independent Highly fault tolerance Incompatible Expensive

Software RAID Run on the server’s CPU Directly depends on server’s CPU speed Occupy host system memory and CPU operation,

degrading CPU performance Cheap

PART II Performance Analyze and

Improvement

Performance Analyze

Aspects:Performance and cost

Metrics to evaluate performanceImplementation and Configuration

Reliability

Reliability Analyze

Reliability Fault Tolerance Availability

Tradeoff

Performance, Reliability and fault tolerance concern

Performance Summary

RAID 0 RAID 1 RAID 5 RADI 10

Read High 2X High High

Write High 1X Medium High

Fault tolerance

No Yes Yes Yes

Disk utilization

High Low High Low

Key problems

Data lost when any disk fails

Use double the disk space

Lower throughput with disk failure

Very expensive, not scalable

Key advantages

High I/O performance

Very high I/O performance

A good overall balance

High reliability with good performance

Implementation Consideration

Avoiding Stale Data When disk fails When invalid logic sector

reconstructed Regenerating Parity after system

Crash Inconsistent mark Parity regenerated

Operating with a failed disk

RAID Level 5 Analyze

Importance Have the best small read, large

read,and large write performance .

Allowing somewhat better parallelism in a multiple-transaction environment

Good fault toleranceWidely Used

RAID 5 Performance Improvement

Improvement on small writeBuffering and caching

Write buffering Read caching

Floating ParityParity logging

Advanced topic

Advanced techniques used in the design of redundant disk arrays. Declustered ParityExploiting On_line spare disksData stripping disk arraysPerformance and reliability modeling

Conclusion

AdvantageHigher Data SecurityFault Tolerance Improved Availability Increased, Integrated Capacity Improved Performance

DisadvantageHigh cost for business

Limitation

How to evaluate whether you should use RAID

Not referring some techniques for back up

Risk to use RAID

Future Work

Be careful to use RAID Decide which level of RAID need to

be used. Make a decision on implementation

of RAID, Hardware RAID or Software RAID

Lower the cost

Questions