Front cover A Look at System i Integrated DASD Configuration and Performance under i5/OS Integrated disk configuration from a performance view Lots of disk performance considerations and tips Featuring the large read/write controllers Jim Cook Sue Baker Brian Podrow Chris Place ibm.com/redbooks Redpaper International Technical Support Organization A Look at System i Integrated DASD Configuration and Performance under i5/OS April 2008 REDP-3919-00 Note: Before using this information and the product it supports, read the information in “Notices” on page v. First Edition (April 2008) This edition applies to Version 5, Release 3, Modification 0 and Version 5, Release 4, Modification 0 of i5/OS. This document created or updated on April 8, 2008. © Copyright International Business Machines Corporation 2008. All rights reserved. Note to U.S. Government Users Restricted Rights -- Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp. Contents Notices . .v Trademarks . vi Preface . vii The team that wrote this IBM Redpaper . viii Become a published author . ix Comments welcome. ix Chapter 1. The importance of disk subsystems to system performance . 1 1.1 Understanding the key components of overall system performance. 2 1.2 Configuration factors affecting disk subsystem performance . 4 1.2.1 Key observations affecting disk performance . 5 Chapter 2. Understanding disk performance . 7 2.1 Some definitions . 8 2.2 Disk drive considerations . 12 2.3 Disk controller considerations . 14 2.4 Other considerations affecting disk sizing, performance, and availability . 15 2.4.1 Overall disk sizing considerations. 15 2.4.2 Mirroring compared to RAID-5 or RAID-6 . 19 2.4.3 The importance of auxiliary write cache . 20 2.4.4 Other disk subsystem functions affecting performance . 21 Chapter 3. Large read and write cache disk controllers and enclosures . 23 3.1 New disk controllers used with existing (#5094/5294) disk towers . 24 3.1.1 Auxiliary write cache features for new #5738/5777 IOAs and older #2757/2780 IOAs . 24 3.1.2 Positioning the February 2007 disk controllers used in #5094/5294 towers. 25 3.2 TotalStorage EXP24 disk enclosure features and capabilities . 26 3.3 Disk controllers that support the EXP24 disk drawer and tower . 29 3.4 Positioning the new disk controllers and EXP24 disk enclosures . 32 Chapter 4. Planning and installation considerations for large cache disk controllers 35 4.1 Minimum code levels. 36 4.2 Feature code to CCIN cross reference . 38 4.3 Card placement rules . 39 4.3.1 5094, 5294, 9094, 9194, and 8294 PCI-X expansion units . 39 4.3.2 5096, 5296 PCI-X expansion units . 42 4.3.3 5790 PCI-X expansion units . 43 4.3.4 5088, 0588 PCI-X expansion units . 43 4.3.5 5095, 0595 PCI-X expansion units . 45 4.3.6 520 POWER5 system units. 47 4.3.7 520 POWER5+ system units . 47 4.3.8 550 POWER5 system units. 48 4.3.9 550 POWER5+ system units . 48 4.3.10 570 POWER5 system units. 49 4.3.11 570 POWER5+ system units . 49 4.3.12 5074, 5079, and 9094 expansion units . 50 © Copyright IBM Corp. 2008. All rights reserved. iii 4.4 Parity set planning. 51 4.4.1 RAID-5 . 51 4.4.2 RAID-6 . 52 4.5 EXP24 disk enclosure and CCIN 571F IOA . 52 4.5.1 EXP24 disk enclosure front and rear views . 54 4.5.2 Feature 5741/5742 Disk Slot Enabler placement and cabling recommendations. 55 4.5.3 Load source drive considerations in #5786/#5787 . 56 Chapter 5. Performance considerations . 59 5.1 Review of performance test results. 60 5.1.1 2780 versus new IOAs . 61 5.1.2 RAID-6 versus RAID-5 . 61 5.1.3 RAID-5 versus mirroring . 62 5.2 Disk controller I/O performance guidelines . 63 Appendix A. System i integrated disk capabilities that require a SAN on other systems . 65 SAN and native System i capabilities. 66 Conclusion . 68 Appendix B. Understanding disk write cache . 69 Appendix C. Understanding RAID-5, RAID-6, and associated performance considerations . 73 A brief history of RAID . 74 The various RAID levels. 74 Appendix D. Mirroring. 85 Mirroring overview . 86 Disk activity and performance during normal mirrored operations. 86 Mirroring performance during disk outage operations . 88 Mirroring performance during disk drive rebuild operations . 89 Recovery from a controller failure with mirrored disk controllers . 90 Using double capacity disks in a mirrored environment. 91 Some conclusions about mirroring implementations on the System i . 92 Appendix E. Additional examples of situations using mixed capacity disk drives . 95 Example 1 . 96 Example 2a . 96 Example 2b . 97 Appendix F. References to articles on future disk technologies and replacements . 99 Appendix G. A real-world approach to sizing disks for adequate performance . 101 Related publications . 111 IBM Redbooks Publications . 111 Online resources . 111 How to get IBM Redbooks Publications . ..