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HP OpenVMS Systems Documentation

Chapter 4 Creating and Managing Shadow Sets Using DCL Commands

HP Volume Shadowing for OpenVMS: OpenVMS Version 8.4

Chapter 4 Creating and Managing Shadow Sets Using DCL Commands

Table of Contents

Allocating Devices

Creating a Shadow Set

Using INITIALIZE/SHADOW/ERASE to Form a Shadow Set (Integrity servers and Alpha)

Benefits and Side Effects of Using /ERASE
Requirements for Using INITIALIZE/SHADOW
INITIALIZE/SHADOW Examples

MOUNT Command Qualifiers for Shadowing

MOUNT Command Qualifiers Specific to Shadowing
Additional MOUNT Command Qualifiers Used for Shadowing
Creating a Shadow Set With /NOASSIST
Creating a Shadow Set With /SYSTEM and With /CLUSTER

Adding Shadow Set Members

Adding a Disk to an Existing Shadow Set
Creating a Two-Member Shadow Set and Adding a Third Member
Checking Status of Potential Shadow Set Members With /CONFIRM
Checking Status of Potential Shadow Set Members With /NOCOPY

Mounting a Shadow Set on Other Nodes in the Cluster

Reconstructing a Shadow Set With /INCLUDE
Mounting a Former Shadow Set Member as a Non-shadowed Disk

Managing Shadow Sets With SET SHADOW (Integrity servers and Alpha)

How to Use the Multiple-Site SET SHADOW and DISMOUNT Command Qualifiers

Managing Copy and Merge Operations (Integrity servers and Alpha)

Using /DEMAND_MERGE to Start a Merge Operation
SHOW SHADOW Management Functions

Prioritizing Merge and Copy Operations

Default Management of Merge and Copy Operations
Hierarchy of Transient State Operations
Assigning Priorities to Shadow Sets
Displaying Shadow Set Priority Values
Controlling Which Systems Manage Merge and Copy Operations
Managing Merge Operations
Managing Copy Operations
Managing Transient States in Progress

Removing Members and Dissolving Shadow Sets

Removing Members from Shadow Sets
Dissolving Shadow Sets
Dismounting Shadow Sets in Site-Specific Shutdown Procedures
Dismounting and Remounting With One Less Member for Backup

Displaying Information About Shadow Sets

Listing Shadow Sets
Listing Shadow Set Members
SHOW DEVICE Examples for Shadow Set Information
Using ANALYZE/DISK/SHADOW to Examine a Shadow Set
Displaying Shadow Set Information With SDA
Obtaining Shadow Set Information With F$GETDVI

This chapter describes how to create, mount, dismount, and dissolve shadow sets using interactive DCL commands. It also describes how to use the DCL command SET SHADOW to manage merge and copy operations and to specify management attributes for shadow set members located at different sites in a multiple-site OpenVMS Cluster system. In addition, it describes how to use the DCL command SHOW DEVICE and the lexical function F$GETDVI to access current information about the state of shadow sets.

Volume Shadowing for OpenVMS improves data availability by ensuring that corresponding logical block numbers (LBNs) on multiple disk volumes contain the same information. Upon receiving a command to mount or dismount disks in a shadow set, the volume shadowing software may need to reconcile data differences and ensure that corresponding LBNs contain the same information.

An understanding of the copy and merge operations used for data reconciliation is essential to the discussions in this chapter. Therefore, you may find it helpful to refer to Chapter 6 to understand how Volume Shadowing for OpenVMS ensures data availability and consistency during changes in shadow set membership.