Second Edition (April 2000)
Part Number: EKHSG85-CG. B01
Compaq Computer Corporation
Notice
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HSG80 Array Controller ACS V8.5 Configuration Guide
Second Edition April 2000
Part Number EKHSG85-CG. B01
Contents
Chapter 1
Planning a Subsystem
Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Controller Designations A and B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Controller Designations "This Controller" and "Other Controller". . . . . . . . . . . . . . . . . . . 13
Selecting a Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Selecting a Cache Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Read Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Read-Ahead Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Write-Back Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Write-Through Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Enabling Mirrored Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
The Command Console LUN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Naming Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Numbers of Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Assigning Unit Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Matching Units to Host Connections in Transparent Failover Mode. . . . . . . . . . . . . . . . . 117
Matching Units to Host Connections in Multiple-bus Failover Mode . . . . . . . . . . . . . . . . 119
Assigning Unit Numbers Depending on SCSI_VERSION . . . . . . . . . . . . . . . . . . . . . . . . 120
The CCL in SCSI-3 mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
The CCL in SCSI-2 Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Restricting Host Access (Selective Storage Presentation). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
iv HSG80 Array Controller ACS Version 8.5 Configuration Guide
Restricting Host Access in Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Restricting Host Access by Separate Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Restricting Host Access by Disabling Access Paths . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Restricting Host Access by Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Restricting Host Access in Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Restricting Host Access by Disabling Access Paths . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Restricting Host Access by Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Worldwide Names (Node IDs and Port IDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Restoring Worldwide Names (Node IDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Chapter 2
Planning Storage
Where to Start.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Configuration Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Device PTL Addressing Convention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Determining Storage Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Choosing a Container Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Creating a Storageset Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Storageset Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
Stripeset Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
Mirrorset Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
RAID set Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Striped Mirrorset Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Partition Planning Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Defining a Partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Guidelines for Partitioning Storagesets and Disk Drives. . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Changing Characteristics through Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Enabling Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Changing Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Storageset Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
RAID set Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Mirrorset Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Partition Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Initialization Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Chunk Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Increasing the Request Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Increasing the Data Transfer Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Increasing Sequential Write Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Save Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Destroy/Nodestroy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Contents v
Unit Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Storage Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Creating a Storage Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Example Storage Map - BA370 Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
Example Storage Map - Model 4214 Disk Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Example Storage Map - Model 4254 Disk Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
Using the LOCATE Command to Find Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
The Next Step... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Chapter 3
Configuration Procedures for Fabric Subsystems
Establishing a Local Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Configuration Procedure Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Configuring a Single Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Cabling a Single controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
CLI Configuration Procedure for a Single Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Configuration Procedure for Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Cabling Controllers in Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
CLI Configuration Procedure for Transparent Failover Mode. . . . . . . . . . . . . . . . . . . . . . . 39
Configuration Procedure for Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
Cabling Controllers in Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
CLI Configuration Procedure for Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . 315
Configuring Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Configuring a Stripeset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Configuring a Mirrorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
Configuring a RAIDset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
Configuring a Striped Mirrorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Configuring a Single-Disk Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Configuring a Partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
Assigning Unit Numbers and Unit Qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
Assigning a Unit Number to a Storageset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
Assigning a Unit Number to a Single (JBOD) Disk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Assigning a Unit Number to a Partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Preferring Units in Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Configuration Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Changing the CLI Prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Adding Disk Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Adding a Disk Drive to the Spareset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Removing a Disk Drive from the Spareset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Enabling Autospare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Deleting a Storageset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
vi HSG80 Array Controller ACS Version 8.5 Configuration Guide
Changing Switches for a Storageset or Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Displaying the Current Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Changing RAIDset and Mirrorset Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Changing Device Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Changing Initialize Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Changing Unit Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Chapter 4
Configuration Procedures for Loop Subsystems
Establishing a Local Connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Configuration Procedure Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Configuring a Single Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Cabling a Single controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
CLI Configuration Procedure for a Single Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Configuration Procedure for Transparent Failover Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Cabling Controllers in Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
CLI Configuration Procedure for Transparent Failover Mode . . . . . . . . . . . . . . . . . . . . . . 410
Configuration Procedure for Multiple-Bus Failover Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Cabling Controllers in Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
CLI Configuration Procedure for Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . 415
Configuring Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Configuring a Stripeset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Configuring a Mirrorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Configuring a RAIDset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
Configuring a Striped Mirrorset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Configuring a Single-Disk Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Configuring a Partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Assigning Unit Numbers and Unit Qualifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Assigning a Unit Number to a Storageset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Assigning a Unit Number to a Single (JBOD) Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
Assigning a Unit Number to a Partition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
Preferring Units in Multiple-Bus Failover Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
Configuration Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
Changing the CLI Prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
Adding Disk Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
Adding a Disk Drive to the Spareset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
Removing a Disk Drive from the Spareset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
Enabling Autospare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
Deleting a Storageset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Changing Switches for a Storageset or Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Displaying the Current Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Contents vii
Changing RAIDset and Mirrorset Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
Changing Device Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
Changing Initialize Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
Changing Unit Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
Chapter 5
Other Procedures
Backing Up the Subsystem Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Cloning Data for Backup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Moving Storagesets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Appendix A
Subsystem Profile Templates
Storageset Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A2
Storage Map Template 1 - BA370 Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A3
Storage Map Template 2 - BA370 Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A4
Storage Map Template 3 - BA370 Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A5
Storage Map Template 4 - Model 4214 Disk Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A6
Storage Map Template 5- Model 4254 Disk Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A7
viii HSG80 Array Controller ACS Version 8.5 Configuration Guide
Figures
Figure 11. Location of controllers and cache modules in a BA370 enclosure. . . . . . . . . . . . . . 12
Figure 12. Location of controllers and cache modules in an Model 2200
controller enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 13. "This controller" and "other controller" in a BA370 enclosure . . . . . . . . . . . . . . . . 13
Figure 14. "This controller" and "other controller" in an Model 2200 controller enclosure . . . 14
Figure 15. Transparent failover - normal operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 16. Transparent failover - after failover from controller B to controller A . . . . . . . . . . 17
Figure 17. Typical multiple-bus configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 18. Mirrored caching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Figure 19. Connections in separate-link, transparent failover mode configurations . . . . . . . . 114
Figure 110. Connections in single-link, transparent failover mode configurations. . . . . . . . . 115
Figure 111. Connections in multiple-bus failover mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Figure 112. LUN presentation to hosts, as determined by offset. . . . . . . . . . . . . . . . . . . . . . . 118
Figure 113. Limiting host access In transparent failover mode . . . . . . . . . . . . . . . . . . . . . . . . 123
Figure 114. Limiting host access in multiple-bus failover mode. . . . . . . . . . . . . . . . . . . . . . . 126
Figure 115. Placement of the worldwide name label in a subsystem in a
BA370 enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Figure 116. Placement of the worldwide name label in a subsystem in an
Model 2200 controller enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Figure 21. PTL naming convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Figure 22. PTL addressing in a configuration in a BA370 enclosure . . . . . . . . . . . . . . . . . . . . 24
Figure 23. PTL addressing in a configuration - using three Model 4214 disk enclosures,
Single-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 24. PTL addressing in a configuration using three Model 4254 disk enclosures,
Dual-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figures ix
Figure 25. Mapping a unit to physical disk drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Figure 26. Container types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 27. An example storageset profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Figure 28. A 3-member RAID 0 stripeset (example 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
Figure 29. A 3-member RAID 0 stripeset (example 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Figure 210. Mirrorsets maintain two copies of the same data . . . . . . . . . . . . . . . . . . . . . . . . 215
Figure 211. Mirrorset example 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Figure 212. A 5-member RAIDset using parity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Figure 213. Striped mirrorset (example 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Figure 214. Striped mirrorset (example 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Figure 215. One example of a partitioned single-disk unit . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Figure 216. Chunk size larger than the request size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Figure 217. Chunk size smaller than the request size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Figure 218. BA370 enclosure - example storage map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Figure 219. Model 4214 disk enclosure - example storage map . . . . . . . . . . . . . . . . . . . . . . 231
Figure 220. Model 4254 disk enclosure - example storage map . . . . . . . . . . . . . . . . . . . . . . 232
Figure 31. Maintenance port connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 32. Configuration flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 33. Single controller cabling with one switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 34. Single controller cabling with two switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 35. Transparent failover cabling with two switches . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 36. Transparent failover cabling with one switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 37. Multiple-bus failover cabling, option 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
Figure 38. Multiple-bus failover cabling, option 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
Figure 39. Multiple-bus failover cabling, option 3 (limited path redundancy) . . . . . . . . . . . 315
Figure 41. Maintenance port connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 42. Configuration flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 43. Single controller cabling with one hub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Figure 44. Single controller cabling with two hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Figure 45. Transparent failover cabling with two hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Figure 46. Transparent failover cabling with one hub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Figure 47. Multiple-bus failover cabling, option 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
Figure 48. Multiple-bus failover cabling, option 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Figure 49. Multiple-bus failover cabling, option 3 (limited path redundancy) . . . . . . . . . . . 415
Figure 51. Steps the CLONE utility follows for duplicating unit members. . . . . . . . . . . . . . . 53
x HSG80 Array Controller ACS Version 8.5 Configuration Guide
Tables
Table 11 Unit Assignments and SCSI_VERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Table 21 A Comparison of Container Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Table 22 Example Chunk Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
About This Guide
This book describes:
I things to consider while planning a configuration
I configuration procedures
This book does not contain information about the operating environments to which the
controller may be connected, nor does it contain detailed information about subsystem
enclosures or their components. See the documentation that accompanied these
peripherals for information about them.
Conventions
This book uses the following special notices and typographical conventions to help you
find what you're looking for:
Special Notices
This book does not contain detailed descriptions of standard safety procedures. However,
it does contain warnings for procedures that could cause personal injury and cautions for
procedures that could damage the controller or its related components. Look for these
symbols when you are carrying out the procedures in this book:
xii HSG80 Array Controller ACS Version 8.5 Configuration Guide
WARNING: A Warning contains information essential to people's safety. It advises
users that failure to take or avoid a specific action could result in physical harm to the
user or hardware. Use a warning, not a caution, when such damage is possible.
CAUTION: A Caution contains information that the user needs to know to avoid
damaging the software or hardware.
IMPORTANT: An important note is a type of note that provides information essential to the
completion of a task. Users can disregard information in a note and still complete a task, but
they should not disregard an important note.
NOTE: A note indicates neutral or positive information that emphasizes or supplements
important points of the main text. A note supplies information that may apply only in special
cases--for example, memory limitations, equipment configurations, or details that apply to
specific versions of a program.
Related Publications
The following table lists some of the documents related to the use of the controller, cache
module, and external cache battery.
Table 1 Relevant Publications
Document Title Part Number
StorageWorks Solutions Software Kit Overview EKSOLSRAA / 166314-001
Compaq StorageWorks HSG80 Array Controller ACS Version 8.5 EKHSG 84SV. B01 / 118620002
Maintenance and Service Guide
Compaq StorageWorks HSG80 Array Controller ACS Version 8.5 EKHSG85RG / 165145001
CLI Reference Guide
Compaq StorageWorks Command Console (HSG80) User's Guide AARFA2DTE / 387405004
Compaq StorageWorks UltraSCSI RAID Enclosure (BA370-Series) EKBA370UG / 387403001
User's Guide
Compaq StorageWorks Fibre Channel Storage Switch Service AARHBZATE / 135268001
Guide
About This Guide xiii
Table 1 Relevant Publications (Continued)
Document Title Part Number
Compaq StorageWorks Fibre Channel Storage Switch User's AARH BYATE / 135267001
Guide
Compaq StorageWorks Fibre Channel Switch Quick Setup Guide AARHC0ATE / 135269001
Compaq StorageWorks Fibre Channel Arbitrated Loop Hub EKDHGGAUG
(DS-DHGGA-CA) User's Guide
Compaq StorageWorks Data Replication Manager HSG80 ACS EKHSG 84DT / 128519002
Version 8.5P Operations Guide
Compaq StorageWorks KGPSA PCI-to-Fibre Channel Host EKKGPSAUG
Adapter
The RAIDBOOK--A Source Book for Disk Array Technology RAID Advisory Board:
I.S.B.N 1-879936-90-9
Compaq StorageWorks RA8000/ESA12000 Storage Subsystem EKSMCPRUG / 387404001
User's Guide
Revision History
First Release: October 1999
Second Release: March 2000
1
Chapter
Planning a Subsystem
The concepts in this chapter will help you plan the configuration of the subsystem. This
chapter is one of two planning chapters; the other planning chapter is Chapter 2, which
presents information about what types of storagesets to choose. When you have planned
both storage and subsystem, Chapter 3 presents a configuration flowchart and a sample
configuration procedure for fabric subsystems; Chapter 4 presents a configuration
flowchart and a sample configuration procedure for arbitrated loop subsystems.
This chapter frequently references the command line interface (CLI). For the complete
syntax and descriptions of the CLI commands, see the Compaq StorageWorks HSG80
Array Controller ACS Version 8.5 CLI Reference Guide.
Terminology
The terms A, B, "this controller", and "other controller" are used to distinguish one
controller from another in a two-controller (also called dual-redundant) subsystem. These
terms are described in the following sections.
Controller Designations A and B
Controllers and cache modules are designated either A or B depending on their location in
the enclosure, as shown in Figure 12.
12 HSG80 Array Controller ACS Version 8.5 Configuration Guide
EMU PVA
Controller A
Controller B
Cache module A Cache module B
CXO6283A
Figure 11. Location of controllers and cache modules in a BA370 enclosure
2 2 2
1 1 1 1 3
1 ECBs
2 Fans
3 EMU
CXO6323C
4 Power supplies
5 I/Omodules
6
5 5 5
Array controllers
5 5 5
7 Cache modules
6
4 4
6
7 7
CXO6325C
Figure 12. Location of controllers and cache modules in an Model 2200 controller enclosure
Planning a Subsystem 1 3
Controller Designations "This Controller" and "Other
Controller"
Some CLI commands use the terms "this" and "other" to identify one controller or the
other in a dual-redundant pair. These designations are a shortened form of "this controller"
and "other controller". These terms are defined as follows:
I "this controller"--the controller that is the focus of the CLI session. "This controller"
is the controller to which the maintenance terminal is attached and through which the
CLI commands are being entered. "This controller"can be shortened to "this" in CLI
commands.
I "other controller"--the controller that is not the focus of the CLI session and through
which CLI commands are not being entered. "Other controller" can be shortened to
"other" in CLI commands.
Figure 13 shows the relationship between "this controller" and "other controller."
1
2
CXO6468D
1 Other controller 2 This controller
Figure 13. "This controller" and "other controller" in a BA370 enclosure
14 HSG80 Array Controller ACS Version 8.5 Configuration Guide
1
2
3
CXO7178A
1 Other controller 2 This controller
Figure 14. "This controller" and "other controller" in an Model 2200 controller enclosure
Selecting a Failover Mode
Failover is a way to keep the storage array available to the host in the event of one
controller becoming unresponsive. A controller can become unresponsive due to a
hardware failure (such as a failure of a host bus adapter or of the controller) or to a failure
of the link between host and controller.Failover keeps the storage array available to the
host(s) by allowing the surviving controller to take over total control of the subsystem.
There are two failover modes:
I transparent, which is handled by the surviving controller and is transparent (invisible)
to the host(s)
I mu ltiple-bus, which is handled by the host(s)
Either mode of failover can work with either topology (loop or fabric).
Transparent Failover Mode
Transparent failover mode has the following characteristics:
I hosts do not know failover has taken place
I units are divided between host ports 1 and 2
Planning a Subsystem 1 5
In transparent failover mode, host port 1 of controller A and host port 1 of controller B
must be on the same Fibre Channel link. Likewise, host port 2 of controller A and host
port 2 of controller B must be on the same Fibre Channel link. Depending on operating
system restrictions and requirements, the port 1 link and the port 2 links can be separate
links, or they can be the same link.
At any one time, only one controller has an active port 1and only on controller has an
active port 2. The other ports are in standby mode. In normal operation, controller A's port
1 is active and controller B's port 2 is active. A representative configuration is shown in
Figure 15. The active and standby ports share port identity, enabling the standby port to
take over for the active one. If one controller fails, its companion controller (known as the
surviving controller) takes over control by making both its host ports active, as shown in
Figure 16.
Units are divided between the host ports:
I Units 0-99 are on host port 1 of both controllers (but accessible only through the active
port)
I Units 100-199 are on host port 2 of both controllers (but accessible only through the
active port)
The limitation of transparent failover is that it only compensates for a controller failure,
and not for failures of either the Fibre Channel link or host Fibre Channel adapters.
16 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Host 1 Host 2 Host 3
Switch or hub Switch or hub
Host Host
Controller A
port 1 port 2
active standby
D0 D1 D100 D101 D120
Host Host
port 1 port 2
Controller B
standby active
CXO7036A
Figure 15. Transparent failover - normal operation
Planning a Subsystem 1 7
Host 1 Host 2 Host 3
Switch or hub Switch or hub
Host Host
Controller A
port 1 port 2
active active
D0 D1 D100 D101 D120
Host Host
port 1 port 2
Controller B
not not
not available
available available
CXO7035A
Figure 16. Transparent failover - after failover from controller B to controller A
18 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Multiple-Bus Failover Mode
Multiple-bus failover mode has the following characteristics:
I host control the failover process by moving the unit(s) from one controller to another
I all units (0 through 199) are visible at all host ports, but accessible only through one
controller at any specific time
I each host has two or more paths to the units
Each host must have special software to control failover. With this software, the host sees
the same units visible through two (or more) paths. When one path fails, the host can issue
commands to move the units from one path to another. A typical multiple-bus failover
configuration is shown in Figure 17.
In multiple-bus failover mode, you can specify which units are normally serviced by a
specific controller of a controller pair. This process is called preferring or preferment.
Units can be preferred to one controller or the other by the PREFERRED_PATH switch of
the ADD (or SET) UNIT command. For example, use the following command to prefer
unit D101 to `this controller':
SET D101 PREFERRED_PATH=THIS_CONTROLLER
NOTE: This is a temporary, initial preference, which can be overridden by the host(s).
Keep the following points in mind when configuring controllers for multiple-bus failover:
I multiple-bus failover can compensate for a failure in any of the following:
controller
switch or hub
Fibre Channel link
host Fibre Channel adapter
I a host can re-distribute the I/O load between the controllers
I all hosts must have operating-system software that supports multiple-bus failover
mode
Planning a Subsystem 1 9
Host 1 Host 2 Host 3
"XANDER" "BUFFY" "WILLOW"
FCA1 FCA2 FCA1 FCA2 FCA1 FCA2
Switch Switch
or hub or hub
Host Host
Controller A
port 1 port 2
active active
D0 D1 D2 D100 D101 D120
All units visible to all ports
Host Host
port 1 port 2
Controller B
active active
NOTE: FCA = Fibre Channel Adapter
CXO7094A
Figure 17. Typical multiple-bus configuration
110 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Selecting a Cache Mode
The cache module supports read, read-ahead, write-through, and write-back caching
techniques. Cache technique is selected separately for each unit. For example, you can
enable only read and write-through caching for some units while enabling only write-back
caching for other units.
Read Caching
When the controller receives a read request from the host, it reads the data from the disk
drives, delivers it to the host, and stores the data in its cache module. Subsequent reads for
the same data will take the data from cache rather than accessing the data from the disks.
This process is called read caching.
Read caching can give improved response time to many of the host's read requests. By
default, read caching is enabled for all units.
Read-Ahead Caching
During read-ahead caching, the controller anticipates subsequent read requests and begins
to prefetch the next blocks of data from the disks as it sends the requested read data to the
host. This is a parallel action. The controller notifies the host of the read completion, and
subsequent sequential read requests are satisfied from the cache memory. By default,
read-ahead caching is enabled for all units.
Write-Back Caching
Write-back caching improves the subsystem's response time to write requests by allowing
the controller to declare the write operation complete as soon as the data reaches cache
memory. The controller performs the slower operation of writing the data to the disk
drives at a later time.
By default, write-back caching is enabled for all units, but only if there is a backup power
source for the cache modules (either batteries or an unterruptible power supply).
Planning a Subsystem 1 11
Write-Through Caching
When the controller receives a write request from the host, it places the data in its cache
module, writes the data to the disk drives, then notifies the host when the write operation is
complete. This process is called write-through caching because the data actually passes
through--and is stored in--the cache memory on its way to the disk drives. Write-through
caching is enabled when write-back caching is disabled.
Enabling Mirrored Caching
In mirrored caching, half of each controller's cache mirrors the companion controller's
cache, as shown in Figure 18.
The total memory available for cached data is reduced by half, but the level of protection if
greater.
Cache module A Cache module B
A B
cache cache
Copy of Copy of
B A
cache cache
CXO5729A
Figure 18. Mirrored caching
Before enabling mirrored caching, make sure the following conditions are met:
I both controllers support the same size cache
I diagnostics indicates that both caches are good
I no unit errors are outstanding, for example, lost data or data that cannot be written to
devices
I both controllers are started and configured in failover mode
112 HSG80 Array Controller ACS Version 8.5 Configuration Guide
The Command Console LUN
The GUI interface, StorageWorks Command Console (SWCC), needs to see a unit (which
from the host's point of view is a logical unit number, or LUN) in order to communicate
with the controller. When a subsystem is new and no storage units have yet been
configured, a fake LUN needs to be created. This is called the Command Console LUN, or
CCL.
To see the state of the CCL, use the SHOW "this controller"/ "other controller" command.
Because the CCL is not an actual LUN, the SHOW UNITS command will not display the
CCL location.
Connections
The term "connection" applies to every path between a Fibre Channel adapter in a host
computer and an active host port on a controller.
Naming Connections
It is highly recommended to give connections names that has meaning in the context of
your particular configuration. One system that works well is to name each connection after
its host, its adapter, its controller, and its controller host port, as follows:
HOST1A1
HOST NAME
PORT
CONTROLLER
ADAPTER
Examples:
A connection from the first adapter in host SPGS that goes to port 1 of controller A would
be called SPGS1A1.
A connection from the third adapter in host LONDON that goes to port 2 of controller B
would be called LONDON3B2.
NOTE: Connection names are can have a maximum of 9 characters.
Planning a Subsystem 1 13
Numbers of Connections
How many connections result from cabling one adapter into a switch or hub depends on
failover mode and how many links the configuration has:
I If a controller pair is in transparent failover mode and the port 1 link is separate from
the port 2 link (that is, ports 1 of both controllers are on one loop or fabric, and port 2
of both controllers are on another), each adapter will have one connection, as shown in
Figure 19.
I If a controller pair is in transparent failover mode and ports 1 and ports 2 are on the
same link (that is, all ports are on the same loop or fabric), each adapter will have two
connection, as shown in Figure 110.
I If a controller pair is in multiple-bus failover mode, each adapter has four connections,
as shown in Figure 111.
114 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Host 2 Host 3
Host 1
"GILES" "MTN"
"REED"
FCA1 FCA1 FCA1
Switch or hub Switch or hub
Connection
REED1A1
Host Host
Controller A Connection
port 1 port 2
GILES1B2
active standby
Connection
MTN1B2
D0 D1 D100 D101 D120
Host Host
port 1 port 2
Controller B
standby active
NOTE: FCA = Fibre Channel Adapter
CXO7081A
Figure 19. Connections in separate-link, transparent failover mode configurations
Planning a Subsystem 1 15
Host 2 Host 3
Host 1
"STONE" "LORD"
"ALEX"
FCA1 FCA1 FCA1
Switch or hub
Connections Connections
ALEX1A1 ALEX1B2
STONE1A1 STONE1B2
LORD1A1 LORD1B2
Host Host
Controller A
port 1 port 2
active standby
D0 D1 D100 D101 D120
Host Host
port 1 port 2
Controller B
standby active
NOTE: FCA = Fibre Channel Adapter
CXO7079A
Figure 110. Connections in single-link, transparent failover mode configurations
116 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Host 1
"ANGEL"
FCA1 FCA2
Switch Switch
or hub or hub
Connection Connection Connection Connection
ANGEL1B1 ANGEL1A1 ANGEL2A2 ANGEL2B2
Host Host
Controller A
port 1 port 2
active active
D0 D1 D2 D100 D101 D120
All units visible to all ports
Host Host
port 1 port 2
Controller B
active active
NOTE: FCA = Fibre Channel Adapter
CXO7080A
Figure 111. Connections in multiple-bus failover mode
Planning a Subsystem 1 17
Assigning Unit Numbers
The unit number is the designation by which the controller keeps track of the unit. Unit
number is a number from 0 - 199 prefixed by a D, which stands for disk drive. A unit can
be presented as different LUNs to different connections. The interaction of a unit and a
connection is determined by several factors:
I failover mode of the controller pair
I the ENABLE_ACCESS_PATH and PREFERRED_PATH switches in the ADD UNIT
(or SET unit) commands
I the UNIT_OFFSET switch in the ADD CONNECTIONS (or SET connections)
commands
I which controller port the connection is attached to
I the SCSI_VERSION switch of the SET this_controller/other_controller command
The considerations for assigning unit numbers are discussed in the following sections.
Matching Units to Host Connections in Transparent Failover
Mode
In transparent failover mode, the ADD UNIT command creates a unit for host
connection(s) to access and assigns it to either port 1 of both controllers or to port 2 of
both controllers.
Unit numbers are assigned to ports as follows:
I 0 - 99 are assigned to host port 1 of both controllers
I 100 - 199 are assigned to host port 2 of both controllers
For example, unit D2 is on port 1 and unit D102 is on port 2.
What LUN number a host connection assigns to a unit is a function of the UNIT_OFFSET
switch of the ADD (or SET) CONNECTIONS command. The relationship of offset, LUN
number, and unit number is as follows:
LUN number = unit number offset
LUN number is relative to the host (what the host sees the unit as)
unit number is relative to the controller (what the controller sees the unit as)
118 HSG80 Array Controller ACS Version 8.5 Configuration Guide
If no value is specified for offset, then connections on port 1 have a default offset of 0 and
connections on port 2 have a default offset of 100.
For example, if all host connections use the default offset values, unit D2 will be presented
to a port 1 host connection as LUN 2 (unit number of 2 minus offset of 0). Unit 102 will be
presented to a port 2 host connection as LUN 2 (unit number of 102 minus offset of 100).
Figure 112 shows how units are presented as different LUNs, depending on the offset of
the host. In this illustration, host connection 1 and host connection 2 would need to be on
host port 1; host connection 3 would need to be on host port 2.
Host Host Host
Controller connection 1 connection 2 connection 3
units Offset: 0 Offset: 20 Offset: 100
LUN 0
D0
LUN 1
D1
LUN 2
D2
LUN 3
D3
LUN 20 LUN 0
D20
LUN 21 LUN 1
D21
D100 LUN 0
D101 LUN 1
D102 LUN 2
D130 LUN 30
D131 LUN 31
CXO6455B
Figure 112. LUN presentation to hosts, as determined by offset
Offsets other than the default values can be specified. For example, unit D17 would be
visible to a host connection on port 1 that had an offset of 10 as LUN 7 (unit number of 17
minus offset of 10). The unit would not be visible at all to a host connection with a unit
offset of 18 or greater, because that offset is not within the units range (unit number of 17
minus offset of 18 is a negative number).
Similarly, unit D127 would be visible to a host connection on port 2 that had an offset of
120 as LUN 7 (unit number of 127 minus offset of 120). The unit would not be visible at
all to a host connection with a unit offset of 128 or greater, because that offset is not within
the units range (unit number of 127 minus offset of 128 is a negative number).
Planning a Subsystem 1 19
An additional factor to consider when assigning unit numbers and offsets is SCSI version.
If the SCSI_VERSION switch of the SET this_controller/other_controller command is set
to SCSI-3, the Command Console LUN (CCL) is presented as LUN 0 to every connection,
superseding any unit assignments. The interaction between SCSI version and unit
numbers is explained further in "Assigning Unit Numbers Depending on
SCSI_VERSION" on page 120.
In addition, the access path to the host connection must be enabled for the connection to
access the unit. See "Restricting Host Access in Transparent Failover Mode," page 121
Matching Units to Host Connections in Multiple-bus
Failover Mode
In multiple-bus failover mode, the ADD UNIT command creates a unit for host
connections to access. All unit numbers (0 through 199) are potentially visible on all four
controller ports, but are accessible only to those host connections for which access path is
enabled and which have offsets in the unit's range.
What LUN number a host connection assigns to a unit is a function of the UNIT_OFFSET
switch of the ADD (or SET) CONNECTIONS command. The default offset is 0. The
relationship of offset, LUN number, and unit number is as follows:
LUN number = unit number offset
LUN number is relative to the host (what the host sees the unit as)
unit number is relative to the controller (what the controller sees the unit as)
For example, unit D17 would be visible to a host connection with an offset of 0 as LUN 17
(unit number of 17 minus offset of 0). The same unit would be visible to a host connection
with an offset of 10 as LUN 7 (unit number of 17 minus offset of 10). The unit would not
be visible at all to a host connection with a unit offset of 18 or greater, because that offset
is not within the units range (unit number of 17 minus offset of 18 is a negative number).
In addition, the access path to the host connection must be enabled for the connection to
access the unit. This is done through the ENABLE_ACCESS_PATH switch of the ADD
UNIT (or SET unit) command.
Which controller of a dual-redundant pair initially accesses the unit is determined by the
PREFERRED_PATH switch of the ADD UNIT (or SET unit) command. Initially
PREFERRED_PATH determines which controller presents the unit as Ready. The other
controller presents the unit as Not Ready. Hosts can issue a SCSI Start Unit command to
move the unit from one controller to the other.
120 HSG80 Array Controller ACS Version 8.5 Configuration Guide
Assigning Unit Numbers Depending on SCSI_VERSION
The SCSI_VERSION switch of the SET this/other controller command determines how
the Command Console LUN (CCL) is presented. There are two choices: SCSI-2 and
SCSI-3. The choice for SCSI_VERSION effects how certain unit numbers and certain host
connection offsets interact.
The CCL in SCSI-3 mode
If SCSI_VERSION is set to SCSI-3, the CCL is presented as LUN 0 to all connections. The
CCL supersedes any other unit assignment. Therefore, in SCSI-3 mode, a unit that would
normally be presented to a connection as LUN 0 is not visible to that connection at all.
The following are recommendations for assigning host connection offsets and unit
numbers in SCSI-3 mode:
I Offsets should be divisible by 10 (for consistency and simplicity)
I Unit numbers should not be assigned at connection offsets (to avoid being masked by
the CCL at LUN 0)
For example, if a host connection has an offset of 20 and SCSI-3 mode is selected, the
connection will see LUNs as follows:
LUN 0 - CCL
LUN 1 - unit 21
LUN 2 - unit 22, etc.
In this example, if a unit 20 is defined, it will be superseded by the CCL and invisible to
the connection.
The CCL in SCSI-2 Mode
Some operating systems expect or require a disk unit to be at LUN 0. In this case, it is
necessary to specify SCSI-2 mode.
If SCSI_VERSION is set to SCSI-2 mode, the CCL floats, moving to the first available
LUN location, depending on the configuration.
Recommendations for assigning host connection offsets and unit numbers in SCSI-2 mode
are as follows:
I Offsets should be divisible by 10 (for consistency and simplicity)
Planning a Subsystem 1 21
I Unit numbers should be assigned at connection offsets (so that every host connection
has a unit presented at LUN 0)
Table 1-2 summarizes the recommendations for unit assignments based on the
SCSI_VERSION switch.
Table 11 Unit Assignments and SCSI_VERSION
SC SI_VERSION Offset Unit Asignment Wha t the connection sees LUN 0 as
SCSI-2 Divisible by 10 At offsets Unit whose number matches offset
SCSI-3 Divisible by 10 Not at offsets CCL
Restricting Host Access (Selective Storage
Presentation)
In a subsystem that is attached to more than one host or if the host(s) have more than one
adapter, it is possible to reserve certain units for the exclusive use by a certain host
connections. For a controller pair, the method used to restrict host access depends on
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