Advanced Topics › VARY Command Serialization

VARY Command Serialization

CA MIA VARY Command Serialization is a software technique designed to maintain tape data integrity during VARY ONLINE Command processing in multi-system tape sharing environments.

CA MIA VARY Command Serialization maintains tape data integrity by:

• Intercepting VARY ONLINE and OFFLINE commands
• Intercepting programmatic calls to IEEVARYD
• Allowing VARY commands and IEEVARYD calls for managed devices to execute when tape data integrity will not be compromised.

CA MIA ONLY allows VARY ONLINE processing for a managed device to occur if the device is:

• Not allocated or in the process of being allocated
• Not the target of a DDR SWAP operation
• Not the target of an UNLOAD command

If VARY ONLINE processing is in progress for a managed device on the local system, CA MIA prevents:

• The device from being allocated on external systems
• The device from being swapped on external systems
• The device from being unloaded on external systems

CA MIA preserves the order of VARY ONLINE and OFFLINE requests to ensure that the device state resulting from a sequence of commands is correct. VARY OFFLINE requests do not require serialization.

CA MIA VARY device serialization software employs z/OS device group locking to maintain tape data integrity on all active systems in a MIMplex. CA MIA Tape Device Allocation, UNLOAD and SWAP serialization also use this cross-system device group locking technique. CA MIA global alignment of VARY, Allocation, UNLOAD and SWAP processing to use this granular, device level serialization minimizes the performance and operational impacts of VARY device serialization.

When a sequence of VARY commands is issued for a device, CA MIA serialization begins when the first VARY ONLINE command is processed. Serialization is maintained until all intercepted VARY ONLINE/OFFLINE commands for the device have been processed.

The operational characteristics associated with the CA MIA enhanced VARY device serialization are discussed in the following sections.