Alternating with other hosts, each host attempts to select requests from the CRQ as long as the host has available recall tasks and the CRQ is not empty. Hosts select the highest priority request that they are capable of processing. Also, hosts select recall requests that are on the host's local queue before requests on the CRQ that are of the same or lower priority. (Requests may be on a host's local queue if the requirements for placement, as mentioned in the previous topic, have not been met.)
When a host selects a request that requires a single ML2 tape, that host processes all single tape requests on the CRQ from that tape. After processing each request from the tape, the processing host selects the next highest priority request that requires that tape. Requests with the same priority are processed in first-in-first-out order. After processing all the requests and after a short wait for any additional requests, the tape is demounted.
If recall requests are unexpectedly not being selected for processing, issue the QUERY ACTIVE command and examine message ARC1541I. A status of anything other than CONNECTED or a hold level of anything other than NONE are probable reasons why certain recall requests are not being selected.
Another cause for certain recall requests not to be selected is that they require an unavailable ML2 tape. If the ML2 tape does not become available within 30 minutes, these requests will time out.