A Look at System i Integrated DASD Configuration and Performance under i5/OS

An IBM Redpaper publication

Published 08 April 2008

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IBM Form #: REDP-3919-00
(126 pages)

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Authors: Jim Cook, Sue Baker, Brian Podrow, Chris Place


This IBM Redpaper publication summarizes integrated DASD configuration, DASD protection capabilities, and DASD performance through the disk controller hardware announced through 2007 and supported by i5/OS V5R3 and V5R4. For the hardware features that we cover in this paper, the information should also apply to later releases.

Note that this publication does not specifically address new disk adapters or any new i5/OS release announced after December 2007.

We feature the large read and write cache disk controllers announced during 1Q 2007 in this paper and include the following information:

-- Specifications of the latest disk controller hardware (including physical placement of the disk controller cards within supporting hardware enclosures)

-- RAID-5, RAID-6, and mirrored protection considerations

-- Positioning the available DASD hardware and protection features

-- Positioning the DASD component contribution to application performance

-- General guidelines for DASD hardware choices based upon estimated disk I/O operation rates with the different protection methods

-- Analyzing DASD performance statistics gathered by i5/OS to see how the environment correlates with the general guidelines

The content of this paper is intended to be used by customers, IBM employees, IBM Business Partners, and others who desire or who need an understanding of disk subsystems in the System i product line.

Table of contents

Chapter 1. The importance of disk subsystems to system performance
Chapter 2. Understanding disk performance
Chapter 3. Large read and write cache disk controllers and enclosures
Chapter 4. Planning and installation considerations for large cache disk controllers
Chapter 5. Performance considerations
Appendix A. System i integrated disk capabilities that require a SAN on other systems
Appendix B. Understanding disk write cache
Appendix C. Understanding RAID-5, RAID-6, and associated performance considerations
Appendix D. Mirroring
Appendix E. Additional examples of situations using mixed capacity disk drives
Appendix F. References to articles on future disk technologies and replacements
Appendix G. A real-world approach to sizing disks for adequate performance

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