eMS also supports Access Method Services to manipulate as and DOS VSAM and SAM data sets. Under eMS, VSAM data sets can span up to nine DASD volumes. CftS does
not support VSAM data set sharing; however, eftS already supports the
sharing of minidisks or full pack minidisks. VSAM data sets created in eMS are not in the eMS file format.
Therefore, CMS commands currently used to manipulate CftS files cannot be
used for VSAM data sets which are read or written in CftS. A VSAft data
set created in CMS has a file format that is compatible with as and DOS VSAM data sets. Thus a VSAM data set created in CMS can later be read
or updated by as or DOS. Because VSAM data sets in CMS are not a part of the CMS file system, eMS file size, record length, and minidisk size restrictions do not
apply. The VSAft data sets are manipulated with Access ftethod Services programs executed under instead of with the CMS file system commands. Also, all VSAM minidisks and full packs used in CMS must be
initialized with the IBCDASDI program; the CMS FORMAT co •• and must not
be used. CMS supports VSAM control blocks with the GENCB, MODCB, TESTCB, and SHOWCB macros.
In its support of VSAM data sets, CMS uses BPS (rotational position
sensing) wherever possible. eMS does not use RPS for 2314/2319 devices,
or for 3340 devices that do not have the feature.
Because CMS support of VSAM data sets is based on DOS/VS VSAM and DOS/VS Access Method Services, only disks supported by DOS/VS can be used for VSAM data sets in eMS. These disks are: • IBM 2314 Direct Access Storage Facility • IBM 2319 Disk Storage • IBM 3330 Disk Storage, Models 1 and 2 • IBM 3330 Disk Storage, Model 11 • IBM 3340 Direct Access storage Facility • IBM 3344 Direct Access Storage • IBM 3350 Direct Access Storage CMS Introduction 2-49

2-50 IBM VM/370 System Logic and Program Determination--Volu.e 2