provides two new JES2 commands, called $ADDEXIT and $REPEXIT, which can be used to dynamically add and replace JES2 user exits without restarting JES2. Note that JES2 must be restarted once to load the new JES2 commands. Then, after this restart, changed exits can be dynamically reloaded with no further JES2 restarts required. 7.5 Spool fencing and affinities The normal mode of operation of JES2 is to allow all jobs to allocate all their track groups across all available spool volumes. This balances the performance and space utilization across the volumes, but results in many jobs being associated with each spool volume. If you wish to stop and remove that volume subsequently, the actual drain process can take a long time because so many jobs are involved. An alternative is to use spool fencing , whereby a job or job class can be limited to using a subset of the volumes. If you have a lot of churn in your DASD farm and find that you frequently move or replace spool volumes, you may be interested in exploring this capability. Refer to "SPOOL partitioning" in z/OS JES2 Initialization and Tuning Guide, SA22-7532, for more information about this topic. There is a similar but different function that you may be interested in if you have multiple sites, with primary DASD in each site. This function allows you to specify an affinity between a given system or set of systems (as opposed to a job or job class) and a SPOOL volume. This gives you the ability to limit the systems in each site to using the DASD that are in the same site, protecting your JES2 environment from connectivity failures or planned site outages. Whereas the association between a job and a SPOOL volume is specified via the FENCE parameter in JES2PARM, the only way to associate a system with a SPOOL volume is by