The FENCE parameter on the SPOOLDEF statement further defines the spooling environment by controlling the partitioning of the spool volumes. Use the FENCE parameter to tell JES2 how to partition spool volumes when performing I/O operations. If fencing is turned off, then jobs that have already obtained some spool space when fencing was active will not be fenced. Use FENCE=(ACTIVE=YES,VOLUMES=nnn) to indicate that all space that a job requires will be allocated from "nnn" volumes. (FENCE=(ACTIVE=YES,VOLUMES=1) is equivalent to FENCE=YES in prior releases.) These volumes are determined by JES2 as the first available volume from which this job can allocate space; this is determined by the setting of the spool partitioning mask work area. The spool partitioning mask is set with bits on to indicate the spool volumes from which the job can allocate space. If you specify FENCE=(ACTIVE=NO,VOLUMES=nnn), the spool partition mask will not indicate any available volumes (no bits are set on). JES2 sets all the bits on (indicating that all volumes are usable) and no spool partitioning is permitted; the space these jobs require is allocated across all available spool volumes.

Although, FENCE=(ACTIVE=YES,VOLUMES=nnn) indicates that JES2 will fence to nnn volumes in most cases more than one nnn volume can be used in certain situations such as when spool volumes fill or if the job obtains spool space on different systems as it goes through different phases. JES2 will allocate space from a subsequent volume(s) when, and if, the "nnn" volumes become full. At that time, JES2 will allocate track groups from the next available volume based on any other criteria that you have defined.