Advanced Topics › VARY Device Serialization › Operational Characteristics of VARY Device Serialization › Overview of Managed Device VARY Processing

Overview of Managed Device VARY Processing

CA MIA intercepts requests to VARY a CA MIA-managed device online or offline. If the request originated from an intercepted z/OS VARY command, then an acknowledgment command response is directed back to the origin console. The VARY device request is then sent to the CA MIA address space for processing. Multiple requests for the same device are maintained in first in, first out order so that online and offline processing are performed in a predictable fashion.

Once the VARY device request is received by the CA MIA address space, a service subtask is attached to process the VARY requests for a given device. Up to eight concurrent VARY device service tasks are attached to perform active VARY device processing. Any additional VARY device requests remain queued by CA MIA until an active VARY device service task completes and is detached. If a given VARY device service task is unduly delayed in obtaining the respective device group lock, then the service task is timed out and the VARY requests for that device are re-queued at the end of those requests that are waiting for be scheduled to a VARY device service task. This time out processing guarantees that VARY device requests that can obtain their respective device group lock are not forced to wait behind those requests that are being delayed for device group locks.

When a given VARY device service subtask completes a VARY device request and the VARY device request originated from an intercepted z/OS VARY command, the results of the VARY device processing are issued as a command response directed back to the origin console. Regardless of the origin of the VARY device request, the results of the VARY device request are logged in SYSLOG by the IBM IEEVARYD service routine that is used by the CA MIA VARY device service subtasks.