FRAGMENTATION: the Condition, the Cause, the CURE by Craig Jensen

ACKNOWLEDGEMENTS

DEDICATION

PREFACE
Who Should Read This Book?
What This Book Can Do for You

INTRODUCTION
The Approach

HOW A DISK WORKS
The Physical Parts of a Disk
Intelligent Disk Controller Functions
Disk-Related Software
Disk File Structures
Disk Performance Terminology
Disk Sets
Disk Architecture Evolution
The Original Problem
The SQUEEZE Solution
The Fragmentation Solution
Summary

WHAT IS FRAGMENTATION?
File Fragmentation and Free Space Fragmentation
Internal Fragmentation
Pagefile Fragmentation
Deliberate and Needful Fragmentation
Why Fragmentation Occurs
Seeing It with Your Own Eyes
Multi-Header Files
The Magnitude of the Fragmentation Problem Today

HOW CAN YOU TELL IF YOU'VE GOT IT?
Fragmentation Analysis Tools

WHAT'S WRONG WITH FRAGMENTATION?
What's Happening to Your Disks?
What's Happening to Your Computer?
What's Happening to Your Applications?
What's Happening to Your Users?

WHAT CAN YOU DO ABOUT IT?
Clear off Disks
Copy / Contiguous
Backup and Restore
Initialization Procedures
Disk-to-Disk Copy
Defragmentation Software Products
Prevention
Preventive Measures When Initializing a Disk
Preventive Measures After a Disk Has Been Initialized
When Would You Not Want to Defragment a Disk?
The Cost of Fragmentation
Conclusion

GETTING THE COMPUTER TO CLEAN UP AFTER ITSELF
History
An On-Line Defragmenter
Safety
Performance
Basic Functionality
Red Herrings
The True Goal of Defragmentation
Who Buys a Defragmenter?
Who Does Not Buy a Defragmenter?
What Does the Future Hold for Defragmentation?
Conclusion

THE ULTIMATE SOLUTION TO THE FRAGMENTATION PROBLEM
Design Goals
Special File Handling
The Impact of Moving Files
What Makes DISKEEPER Unique?
Conclusion

APPENDIX A
What Is a Computer?

APPENDIX B
File Fragmentation Cost Analysis

APPENDIX C
How to Get a Company to Spend Money for Something You Need and Want

GLOSSARY

INDEX

Figure 1 File Fragmentation
Figure 2 Free Space Fragmentation
Figure 3 Record Space Fragmentation
Figure 1-1 A Disk
Figure 1-2 Disk Surface
Figure 1-3 Bit
Figure 1-4 Byte
Figure 1-5 Block
Figure 1-6 Cluster
Figure 1-7 Tracks
Figure 1-8 Platters
Figure 1-9 Cylinder
Figure 1-10 Head
Figure 1-11 Arms
Figure 1-12 Spindle
Figure 1-13 Electronics
Figure 1-14 Disk Drive
Figure 1-15 Cable
Figure 1-16 Seek Ordering
Figure 1-17 Data Caching
Figure 1-18 Physical Block Numbers
Figure 1-19 Logical Block Numbers
Figure 1-20 Storage Bitmap Relationship to Clusters
Figure 1-21 Extents
Figure 1-22 Extent Cache
Figure 1-23 File With One Extent
Figure 1-24 Index File Pointing to Extents
Figure 1-25 Directory
Figure 1-26 Seek Time
Figure 1-27 Rotational Latency
Figure 1-28 Seek Time + Rotational Latency
Figure 1-29 Volume Set
Figure 1-30 Shadow Set
Figure 1-31 Stripeset
Figure 1-32 SQUEEZE
Figure 2-1 Pagefile Fragmentation
Figure 2-2 Contiguous Files on a Disk
Figure 2-3 Fragmented Files on a Disk
Figure 2-4 New File Allocation
Figure 2-5 Extent Cache
Figure 4-1 Disk
Figure 4-2 Disk with File in Two Parts
Figure 4-3 Two File Extents on Different Tracks
Figure 4-4 File in Many Fragments
Figure 6-1 Single Disk
Figure 6-2 Two-Spindle Disk

Example 1-1 Drivers in the OpenVMS Hierarchy
Example 1-2 File with One Retrieval Pointer
Example 1-3 File with Four Retrieval Pointers
Example 3-1 MONITOR IO Display
Example 3-2 MONITOR FCP Display
Example 3-3 SPM SYSTEM Report
Example 3-4 SPM Disk Space Report
Example 3-5 VPA Output Showing Window Turns
Example 3-6 VPA Report Showing Split I/Os
Example 3-7 DAU Output
Example 4-1 MONITOR MODES Display

Table 1-1 Time Required to Access Every Block on a Disk
Table 5-1 Wasted Space Due to Cluster Size Setting

Graph 6-1 Percentage of Vax Sites with a Defragmenter
Graph 6-2 Average Disk Capacity Per System

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