8464axJES3.fm Draft Document for Review February 7, 2020 3:15 pm Selecting UNITNAMEs New or modified data sets Old data sets DFSMS catalog processing For a DD request, the LDG selection is based on the following conditions: GLYPH<SM590000> When all devices in the complex are eligible to satisfy the request, the complex-wide  LDGW3495 name is used. GLYPH<SM590000> When the list of names contains names of all devices of one device type in the complex,  the corresponding complex-device type name (for example, LDG3490E) must be used. GLYPH<SM590000> When the list of names contains all subsystems in one TS3500 tape library, the  library-specific LDG name (in the examples, LDGF4001, LDGF4006, and so on) is used. GLYPH<SM590000> When the list contains only subsystems for a specific device type within one TS3500 tape  library, the LDG device type library name (in the example, LDKF4001, and so on) is used. GLYPH<SM590000> DFSMS managed user catalogs GLYPH<SM590000> JES3-managed user catalogs For new data sets, ACS directs the allocation by providing Storage Group (SG), SC, and Data  Class (DC). When the SG specified by ACS is defined in the active DFSMS configuration as a  tape SG, the request is allocated to a TS3500 tape library tape drive.  DFSMS managed  DISP=MOD  data sets are assumed to be new update locate processing. If a  catalog locate determines that the data set is  old  by the VOLSER specified, a new LDG name  is determined based on the rules for old data sets. Old data set allocations are directed to a specific TS3500 tape library when the volumes  containing the data set are within that TS3500 tape library. For old data sets, the list is  restricted to the TS3500 tape library that contains the volumes. JES3 catalog processing determines all of the catalogs that are required by a job and divides  them into two categories:  DFSMS catalog services, a subsystem interface call to catalog locate processing, is used for  normal locate requests. DFSMS catalog services are started during locate processing. It  starts supervisor call (SVC) 26 for all existing data sets when DFSMS is active.  Locates are required for all existing data sets to determine whether they are DFSMS  managed, even if  VOL=SER=  is present in the DD statement. If the request is for an old data set,  catalog services determine whether it is for a library volume. For multivolume requests that  are system-managed, a check is made to determine whether all volumes are in the same  library. 842  IBM TS7700 Release 5.0 Guide