Introduction › Multisystem Considerations

Multisystem Considerations

In a multisystem environment, physical tape data sets may not be concurrently accessed by more than one system at a time. A tape created on one system can only be read or modified on a different system after the first system has released it. CA Vtape fully supports this environment. Each CA Vtape subsystem can access a specific Virtual Volume as often as required, but only one subsystem can access a specific Virtual Volume at a time.

You can run up to eight CA Vtape subsystems within a single Logical Partition (LPAR) at the same time. Each subsystem runs in its own set of address spaces and must be assigned a unique range of Virtual Device addresses. Once assigned and varied online by one of the subsystems, the Virtual Device addresses cannot be used by other subsystems in the same LPAR.

The same Virtual Device address range can be defined on multiple LPARs for the use of a single CA Vtape subsystem on each LPAR. These devices should not be defined as shared in the operating system hardware configuration definitions or in an automatic tape switching product such as CA MIA or IBM's Tape Auto Switch. Virtual Devices 0100-010F on LPAR A are not the same Virtual Devices as 0100-010F on LPAR B since they are controlled by separate subsystems. Each of these devices can be on-line and actively servicing virtual tape mounts on both LPARs at the exact same time. The only restriction is that they cannot mount the same Virtual Volume at the same time.

A CA Vtape Complex is created when multiple CA Vtape subsystems in the same LPAR or in different LPARs share the same DASD buffer and control data sets. Virtual Volumes written to the DASD buffer by a subsystem participating in a CA Vtape Complex can be read or written by any other subsystem participating in the same CA Vtape Complex.

If all the subsystems on all LPARs in a CA Vtape Complex have access to the same physical tape, any subsystem in those LPARs can recall a Virtual Volume from physical tape to the DASD buffer. If all the LPARs do not have access to the same physical tape, a subsystem with access to the physical tape can be configured as a Recall Server. The Recall Server will perform all recalls for its client subsystems.

The same is true for Externalization (automatic stacking). If all the LPARs have access to physical tape, each subsystem can perform its own externalizations. If all the LPARs do not have access to physical tape, one subsystem can be configured as the Primary Externalization Server. The Primary Externalization Server will perform Externalization for all subsystems in the complex. Secondary or Failover Externalization Servers can also be configured.

The Externalization and Recall Servers exploit some SYSPLEX capabilities but can also run in a non-SYSPLEX environment. The main benefit of this feature is to lower the physical drive requirements and to concentrate their use to a single subsystem in a single LPAR.

A SYSPLEX is not required to support a CA Vtape Complex. Some CA Vtape features will not be fully exploited unless CA MIM or IBM's GRS is able to propagate enqueues across all the LPARs where CA Vtape is implemented.