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.