skip book previous and next navigation links
go up to top of book: HP Volume Shadowing for OpenVMS HP Volume Shadowing for OpenVMS
go to beginning of chapter: Introduction to Volume Shadowing for OpenVMS Introduction to Volume Shadowing for OpenVMS
go to previous page: Overview Overview
go to next page: Hardware EnvironmentHardware Environment
end of book navigation links

Volume Shadowing Tasks and Operations   



The primary volume shadowing operations used to create shadow sets and to maintain consistent data on each member are mount, copy, assisted copy, minicopy (introduced with OpenVMS Version 7.3), merge, and minimerge. When these operations are in progress, the system continues to process read and write requests, thus providing continuous availability.

All volume shadowing operations, except for merges and minimerges, are under the control of the system manager. Merges and minimerges are started automatically by the volume shadowing software if a hardware or software failure occurs that could affect the consistency of the data on the shadow set members.

System managers turn on volume shadowing with the SHADOWING system parameter. They can control the number of concurrent merge or copy operations on a given node by the SHADOW_MAX_COPY system parameter. These volume shadowing system parameters, and all other system parameters used with volume shadowing, are described in Volume Shadowing Parameters and in Write Bitmap System Parameters.

Volume Shadowing for OpenVMS is never invoked directly. Instead, you invoke the DCL commands MOUNT and DISMOUNT. The MOUNT command works with the volume shadowing software to create shadow sets. The DISMOUNT command works with the volume shadowing software to remove shadow set members and to dissolve entire shadow sets.

HSJ and HSC controllers, when present in a configuration, provide software assists for the minimerge and assisted copy operations.

OpenVMS also provides a programming interface for creating and managing shadow sets with the $MOUNT, $DISMOU, and $GETDVI system services. This programming interface is described in Creating and Managing Shadow Sets with System Services.

Main Volume Shadowing Tasks, Operation Name, and Related Software shows the main volume shadowing tasks, the operations associated with them, and the software used to perform the operation. These operations are described in more detail in Creating and Managing Shadow Sets Using DCL Commands, Ensuring Shadow Set Consistency, and Using Minicopy for Backing Up Data (Alpha).

Table 1   Main Volume Shadowing Tasks, Operation Name, and Related Software
Task Operation Software Used
Create a single-member shadow set.
Mount
MOUNT/SHADOW command with the SHADOWING system parameter set.
Create a multiple-member shadow set
Mount and copy
MOUNT/SHADOW command with the SHADOWING system parameter set. When a second or third member is added, the shadowing software starts a copy operation automatically.
Remove a member from a shadow set.
Dismount a device
DISMOUNT command.
Dissolve a shadow set.
Dismount the shadow set (specify its virtual unit name)
DISMOUNT command.
Ensure that the data is identical on all shadow set members in the event of a hardware failure.
Merge or minimerge
Shadowing software does this automatically when it detects a hardware or software failure. If an HSJ or HSC controller is present in the configuration, a minimerge might be done.
Return a dismounted shadow set member to the shadow set.
Copy, assisted copy, or minicopy
MOUNT command, with shadowing software that initiates either a copy or, if properly configured, a minicopy.


go to previous page: Overview Overview
go to next page: Hardware EnvironmentHardware Environment