Draft Document for Review February 7, 2020 3:15 pm 8464axJES3.fm Figure C-11 JES3 CI and MDS processing phases JES3/DFSMS processing DFSMS system-managed tape devices are not selected by using the UNIT parameter in the  JCL. For each data definition ( DD ) request requiring a TS3500 tape library unit, a list of device  pool names is passed, and from that list, an LDG name is assigned to the DD request. This  results in an LDG name passed to JES3 MDS for that request. Device pool names are never  known externally. DFSMS is called by the z/OS interpreter to perform these functions: GLYPH<SM590000> Update the scheduler work area (SWA) for DFSMS tape requests. GLYPH<SM590000> Call ACS exits for construct defaults. Appendix C. JES3 examples and information  841