PERCENTVALID calculation

The PERCENTVALID calculation determines the valid data that exists within an entire connected set; it doesn't determine valid data for an individual volume within that set (unless the connected set consists of a single volume).

In determining whether to recycle a connected set, DFSMShsm by default requires the first tape within the connected set to meet the current PERCENTVALID specification before continuing with the calculation. To allow connected sets to be recycled sooner, and possibly free up more volumes to scratch or tape pools, you can bypass this first volume check by entering the RECYCLE command with the CHECKFIRST parameter specified as N (no). When you specify CHECKFIRST(N), DFSMShsm calculates the percent valid of the entire connected set, regardless of how much valid data is on the first volume of the connect set.

Note that CHECKFIRST(N) causes recycle processing to always determine the average percentage valid for a connected set, which can slow recycle performance if your installation has many large connected sets. Also, if you enter the RECYCLE command with the VOLSER parameter, the system ignores the CHECKFIRST parameter.

Examples

    Volser   % Valid   Predecessor  Successor
    ------   -------   -----------  ---------
    TAPEA      35         -NONE-      TAPEB
    TAPEB       5         TAPEA       -NONE-

If RECYCLE ALL PERCENT(30) EX is issued, the TAPEA–TAPEB connected set will not be selected, since the first tape in the set does not meet the PERCENTVALID criterion and CHECKFIRST(N) was not specified.

    Volser   % Valid   Predecessor  Successor
    ------   -------   -----------  ---------
    TAPEC      25         -NONE-      TAPED
    TAPED      75         TAPEC       -NONE-

If RECYCLE ALL PERCENT(30) EX is issued, the TAPEC–TAPED connected set will not be selected. Even though the first tape in the set meets the PERCENTVALID criterion, the entire connected set does not meet the criterion.

    Volser   % Valid   Predecessor  Successor
    ------   -------   -----------  ---------
    TAPEE       5         -NONE-      TAPEF
    TAPEF      45         TAPEE       -NONE-

If RECYCLE ALL PERCENT(30) EX is issued, the TAPEE–TAPEF connected set will be selected: the first tape volume in the set meets the PERCENTVALID criterion, and the entire connected set meets the criterion.

    Volser   % Valid   Predecessor  Successor
    ------   -------   -----------  ---------
    TAPEG 		   55 	      -NONE- 	    TAPEH
    TAPEH 		    1 	  	   TAPEG       -NONE-

If RECYCLE ALL PERCENT(30) EX CHECKFIRST(N) is issued, the TAPEG-TAPEH connected set will be selected. Although the first tape, TAPEG, does not meet the PERCENTVALID criterion, CHECKFIRST(N) was specified, and the entire connected set meets the PERCENTVALID criterion.