HP Volume Shadowing for OpenVMS ensures that data
is available for applications and end users by duplicating data on
multiple disks. Because the same data is recorded on multiple disk
volumes, if one disk fails, the remaining disk or disks can continue
to service I/O requests. This ability to shadow disk volumes is sometimes
referred to as disk mirroring.
Volume shadowing supports the clusterwide shadowing
of a variety of storage systems. Volume shadowing also supports shadowing
of all mass storage control protocol (MSCP) served disks. For more
information about Volume Shadowing supported devices, see the Volume
Shadowing for OpenVMS Software Product Description.
You can mount multiple compatible disk volumes,
including the system disk, to form a shadow
set. Each disk in the shadow set is known as a shadow set member. Volume Shadowing for OpenVMS logically
binds the shadow set devices together and represents them as a single
virtual device called a virtual unit. This means that multiple members of the shadow set, represented
by the virtual unit, appear to applications and users as a single,
highly available disk.
Volume Shadowing features include:
Shadow set members can be located on any node in an OpenVMS Cluster
that has Volume Shadowing enabled.
shadow-set maintenance functions.
Ability to survive controller,
disk, and media failures transparently.
Shadowing functions that
do not affect application I/O.
Applications and users read and write data to
and from a shadow set using the same commands and program language
syntax and semantics that are used for nonshadowed I/O operations.
Volume shadowed sets are managed and monitored using the same commands
and utilities that are used for nonshadowed disks. The only difference
is that access is through the virtual unit, not to individual devices.
SHDRIVER, the driver that controls the virtual
unit functions, is described in “Driver Functions”.
For more detailed information on HP Volume Shadowing
for OpenVMS, see the Volume Shadowing for