AIX Logical Volume Manager, from A to Z: Introduction and Concepts Laurent Vanel, Ronald van der Knaap, Dugald Foreman, Keigo Matsubara, Antony Steel International Technical Support Organization www.redbooks.ibm.com SG24-5432-00 SG24-5432-00 International Technical Support Organization AIX Logical Volume Manager, from A to Z: Introduction and Concepts December 1999 Take Note! Before using this information and the product it supports, be sure to read the general information in Appendix F, “Special notices” on page 391. First Edition (December 1999) This edition applies to AIX Version 4.3, Program Number 5765-C34. Comments may be addressed to: IBM Corporation, International Technical Support Organization Dept. JN9B Building 003 Internal Zip 2834 11400 Burnet Road Austin, Texas 78758-3493 When you send information to IBM, you grant IBM a non-exclusive right to use or distribute the information in any way it believes appropriate without incurring any obligation to you. © Copyright International Business Machines Corporation 1999. All rights reserved. Note to U.S Government Users – Documentation related to restricted rights – Use, duplication or disclosure is subject to restrictions set forth in GSA ADP Schedule Contract with IBM Corp. Contents Preface. 9 The team that wrote this redbook. 9 Comments welcome. 10 Chapter 1. Components of the logical volume manager . 1 1.1 Overview . 2 1.2 The logical volume storage concepts . 5 1.2.1 Physical volumes . 6 1.2.2 Disk Independence. 13 1.2.3 The physical volume identifier (PVID) . 14 1.2.4 Physical Volume Layout . 15 1.2.5 Maximum number of physical partitions per physical volume . 17 1.2.6 Increasing number of physical partitions per physical volume . 18 1.2.7 Volume groups . 22 1.2.8 Logical volumes . 44 1.2.9 Mirroring. 60 1.2.10 Striping. 60 1.2.11 The ODM . 61 1.3 Operation of the logical volume manager . 70 1.3.1 High-level commands . 71 1.3.2 Intermediate-level commands. 71 1.3.3 Logical Volume Manager subroutine interface library . 72 1.3.4 Introduction to device drivers . 75 1.3.5 Logical volume device driver . 76 1.3.6 Disk device driver . 80 1.3.7 Adapter device driver . 83 1.4 Use of the logical volume manager. 83 1.4.1 Planning your use of volume groups . 83 1.4.2 Planning your use of logical volumes . 86 1.5 Limits . 99 Chapter 2. Mirroring . 101 2.1 Principles . 101 2.1.1 Only logical volumes are mirrored . 101 2.1.2 Each logical volume can have up to three copies . 101 2.1.3 Keep it simple. 103 2.2 Concepts . 105 2.2.1 The allocation policy. 105 2.2.2 The scheduling policy . 111 2.2.3 Availability . 115 2.3 Practical examples . 128 © Copyright IBM Corp. 1999 3 2.3.1 Example configurations . 128 2.4 Mirroring of the rootvg . 132 2.4.1 Brief explanation about the AIX boot sequence . 133 2.4.2 Contiguity of the boot logical volume . 134 2.4.3 Dump device . 135 Chapter 3. Striping . 137 3.1 Concept . 137 3.1.1 Basic schema of the striped logical volumes. 137 3.1.2 Inter physical volume allocation policy . 141 3.1.3 The reorganization relocation flag. 145 3.1.4 Creation and extension of the striped logical volumes . 147 3.1.5 Prohibited options of the mklv command with striping. 150 3.1.6 Prohibited options of the extendlv command with striping . 152 3.1.7 Summary . 152 3.2 Real examples . 152 3.2.1 Example configurations . 152 3.2.2 How to create the striped logical volumes. 153 3.2.3 How to extend the striped logical volumes . 158 3.2.4 Erroneous situations. 161 3.3 The mirror and stripe function. 162 3.3.1 Super strict allocation policy . 163 3.3.2 How to manage a mirrored and striped logical volume . 168 Chapter 4. Concurrent access volume groups . 183 4.1 Concept . 183 4.1.1 Basic schema of the concurrent access . 183 4.1.2 Concurrent access capable and concurrent mode . 185 4.1.3 Concurrent Logical Volume Manager (CLVM) . 187 4.1.4 Limitations . 193 4.2 Real examples . 195 4.2.1 Example configuration . 195 4.2.2 Defining shared LVM components for concurrent access . 198 4.2.3 Installing the HACMP concurrent resource manager (CRM) . 200 4.2.4 Installing HACMP cluster configurations: Standard method . 203 4.2.5 Managing shared logical volumes for concurrent access . 209 4.2.6 Static ODM update method. 210 4.2.7 Dynamic ODM update method . 211 4.3 Shared disk environment solutions . 219 4.3.1 HACMP and HACMP Enhanced Scalability (ES). 219 4.3.2 Cluster lock manager . 223 4.3.3 Shared disk solution on an RS/6000 SP system . 226 4.3.4 What is the HC daemon? . 228 4 AIX Logical Volume Manager, From A to Z: Introduction and Concepts 4.4 History of the concurrent access . 231 Chapter 5. The AIX journaled file system . 233 5.1 What is a journaled file system? . 233 5.2 The JFS structure. 234 5.2.1 The superblock. 234 5.2.2 Logical blocks. 235 5.2.3 Disk i-nodes . 235 5.2.4 Disk i-node structure. 236 5.2.5 i-node addressing . 238 5.2.6 Fragments . 241 5.2.7 Fragments and number of bytes per i-node (NBPI) . 242 5.2.8 Allocation bitmaps . 247 5.2.9 Allocation groups . 247 5.2.10 Allocation in compressed file systems. 251 5.2.11 Allocation in file systems with another fragment size . 251 5.2.12 Allocation in file systems enabled for large files . 252 5.3 How do we use a journaled file system?. 253 5.3.1 The JFS log . 253 5.4 File handling. 254 5.4.1 Understanding system call execution . 254 5.4.2 The logical file system . 255 5.4.3 Virtual file system overview . 257 5.4.4 Understanding virtual nodes.