Draft Document for Review February 7, 2020 3:15 pm 8464axJES3.fm Scratch allocation assistance enablement considerations Complete the following installation steps to prevent job failures from occurring: 1. Ensure that all systems in the JES3plex are at z/OS V2R2 (this is needed because  pre-execution and job execution can occur on different systems in the JES3plex).  However, JES3 itself can be at a lower release level. 2. Make JES3 INISH deck changes as described in INISH deck example. The INISH deck  changes define the library-specific distributed names that are associated with the  distributed libraries clusters in a TS7700. All TS7700 tape drives used by JES3 (with  devices connected to the host) should have the new esoteric names that are defined,  regardless of whether the TS7700 is part of a single or a multi-cluster grid. 3. Roll out the JES3 INISH deck changes to all systems in the JES3plex (this roll-out can  occur one system at a time). The new esoteric names are not passed to JES3 until the  support is enabled through  DEVSUPxx . 4. Enable the support to the host through the  DEVSUPxx PARMLIB  member by using the  JES3_ALLOC_ASSIST=YES  keyword (either at IPL or through the  SET DEVSUP=xx  operator  command). The  SET DEVSUP=xx  operator command can be used to enable this support by  routing the command to all systems in the JES3plex. After this support is enabled, the new  library-specific distributed names can be returned to JES3.  5. Then, unlike the specific allocation assistance support, the scratch allocation assistance  support must be explicitly enabled at the library through the  LIBRARY REQUEST,composite-libraryname,SETTING,DEVALLOC,SCRATCH,ENABLE  command  (disabled by default), and then policies must be set up at the library (on an MC basis) to  request the support for a specific scratch allocation.  Ensure that steps 2 and 3 are completed before enabling this support. Otherwise, job  failures can occur if JES3 does not understand the new esoteric names being passed  (because they were not defined in the JES3 INISH deck). Before assigning an MC policy that uses the scratch allocation assistance support  (specifies candidate clusters), ensure that step 4 is completed first. This helps ensure that  the list of eligible devices that JES3 gets back matches the list of devices that MVS  allocation got back during job run time. Even though MVS allocation has retry logic to try  to circumvent  ABEND05C-309 , that retry logic is not guaranteed to succeed. Here is an example of an INISH deck for a TS7700 multi-cluster grid that has devices online in  two clusters (other clusters whose devices are not connected to the host might exist for  replication purposes). In this example, the composite library has library identification number  X'12345'  and the first distributed library in the grid has library identification number  X'10001' and the second distributed library in the grid has library identification number  X'10002' .  In this example, each distributed library in the grid has 256 devices for a total of 512. The  changes that must be made to the INISH deck to use the optional allocation assist support in  JES3 are shown in  bold italic  text. The INISH deck changes are needed only if the allocation  assist functions are to be enabled by specifying  JES3_ALLOC_ASSIST=YES  in the  DEVSUPxx  PARMLIB  member.  Before you enable the allocation assist functions, ensure that all TS7700 tape drives in the  INISH deck are defined with the necessary  LDXxxxxx  names, even if the TS7700 is a  stand-alone configuration consisting of one distributed library. In this example, rather than the  device statement representing the composite library (as a whole), the device statements are  defined at the distributed (or cluster) level and  LDXxxxxx  names are added (as needed) for  each distributed library in a TS7700 that has devices that are connected to the JES3 host. INISH deck example Appendix C. JES3 examples and information  847