Types of hosts used in a common recover queue

The master scheduler (MS) is the DFSMShsm host that manages all of the volume restore requests in the Common Recover Queue (CVQ). All volume restore requests are sent to the master scheduler, and it assigns work to all of the other hosts eligible in the group to process requests from the CVQ. Each group needs a master scheduler to manage CVQ processing for the group; otherwise, volume restore requests are processed locally.

The other principal types of DFSMShsm hosts are the submitting host and the processing host.

Submitting host
Host that receives requests from commands and, using XCF messaging, sends it to the master scheduler host. Performs command complete processing and posts the user that the command has completed.
Master scheduler (MS)
  • Accepts requests from submitting host members and locally submitted requests, and maintains them as a single common queue of all requests for the CVQ function. The MS can be the submitting host. In this case, the command is not sent
  • Assigns the requests to the available tasks across all of the eligible hosts (processing hosts) that are connected to the CVQ, while balancing the requests among all the hosts.
  • Manages "work completed" messages received from a processing host to support functions like stacking.
  • Sends "command complete" messages back to the submitting host.
Processing host
  • Receives assigned work requests from the master scheduler and places them on its local queue for processing.
  • Sends "work complete" messages back to the master scheduler with specific protocols to support functions like stacking.
  • The processing host could be the submitting host and/or the master scheduler host.
Figure 1, shows a CVQ group where:
  • HSM1 is the submitting and processing host
  • HSM2 is the master scheduler and processing host. It receives all requests, manages them on a single queue, and distributes the requests among the eligible hosts connected to the common queue, through XCF messaging.
  • HSM3 is a processing host.
Figure 1. CVQ Host Types
Illustration of CVQ host types