Determining the structure size of the common recall queue

The common recall queue needs to be sized such that it can contain the maximum number of concurrent recalls that may occur. Due to the dynamic nature of recall activity, there is no exact way to determine what the maximum number of concurrent recall requests may be.

Guideline: Use an INITSIZE value of 5120KB and a SIZE value of 10240KB.

A structure of this initial size is large enough to manage up to 3900 concurrent recall requests with growth up to 8400 concurrent recalls. These values should be large enough for most environments. Table 1 shows the maximum number of recalls that may be contained in structures of various sizes. No structure of less than 2560KB should be used.

Note: The maximum number of recall requests that may be contained within a structure is dependent on the number of requests that are from a unique Migration Level 2 tape. The figures shown in Table 1 are based on 33% of the recall requests requiring a unique ML2 tape. If fewer tapes are needed, then the structure will be able to contain more recall requests than is indicated.

Table 1. Maximum Concurrent Recalls
Structure Size	Maximum Concurrent Recalls
2560KB	1700
5120KB	3900
10240KB	8400
15360KB	12900

It should be recognized that the utilization percentage of the common recall queue will be low most of the time. This is because the average number of concurrent requests will be much lower than the maximum number of concurrent requests. In order to be prepared for a high volume of unexpected recall activity, the common recall queue structure size must be larger than the size needed to contain the average number of recall requests.