CMS VSAM and Access Method Services Planning Considerations for CMS VSAM and
Access Method Services CMS supports interactive program development for
using VSAM. CMS supports VSAM for as programs OS/VS COBOL, or as PL/I programming languages; or
in DOS/VS COBOL or DOS PL/I programming languages. VSAM for as or nos assembler language programs.
as and DOS programs
written in VS BASIC, DOS programs written CMS does not support CMS also supports access method services to manipulate as and DOS VSAM and SAM data sets. Under CMS, VSAM data sets can span up to nine DASD volumes. CMS does
not support VSAM data set sharing; however, CMS already supports the
sharing of minidisks or full pack minidisks. Only one user may have
write access to the VSAM master catalog, but many other users may read
and reference the catalog at the same time. VSAM data sets created in CMS are not in the CMS file format.
Therefore, CMS commands currently used to manipulate CMS files cannot be
used for VSAM data sets that are read or written in CMS. A VSAM data
set created in CMS has a file format that is exactly the same as, and
therefore 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 eMS file system, eMS file size, record length, and minidisk size restrictions do not
apply. The VSAM data sets are manipulated with access method services
programs executed under CMS, instead of with the eMS file system
commands. Also, all VSAM minidisks and full packs used in eMS must be
initialized with the IBCDASDI program or an appropriate DOS/VS or OS/VS disk initialization program (if the minidisk is a full pack); the eMS FORMAT command must not be used.
In its support of VSAM data sets, eMS uses RPS (rotational position
sensing) wherever possible. eMS does not use RPS for 2314/2319 devices,
or for 3340 devices that do not have the feature.
Hardware Devices Supported
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 or for CMS disk files used as input by access
method services. These disks are: IBM 2314 Direct Access Storage Facility IBM 231Q 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 Part 1. Planning for System Generation 31
CMS VSAM and Access Method Services IBM 3350 Direct Access storage When VM/370 MSS support is installed, and the VM/370 processor is
attached to an MSS, the CMS disk may be defined as a 3330 Model 1
which is mapped by VM/370 to all or part of a 3330V volume.
Programming Languages Supported CMS supports VSAM for programs written for the following compilers: OS/VS COBOL Compiler and Library as COBOL Interactive Debug VS Basic Processor as PL/I Optimizing Compiler and Libraries as PL/I Checkout Compiler DOS/VS COBOL Compiler and Library DOS PL/I Optimizing Compiler and Library
Data Set Compatibility Considerations 1.2. 57qO-CB1 573q-CBq 57q8-II1 5734-PL3 5734-PL2 57q6-CBl 5736-PL3 CMS can read and update VSAM data sets that vere created under DOS/VS or OS/VS. In addition, VSAM data sets created under CMS can be read and
updated by DOS/VSE or OS/VS. However, if you perform allocation on a minidisk in CMS, you cannot
use that minidisk in an os virtual machine in any .anner that causes
further allocation. DOS/VS VSAM (and thus CMS) ignores the format-5,
free space DSCB on VSAM disks when it allocates extents. If allocation
later occurs in an as machine, os attempts to create an accurate
format-5 DSCB. However, the format-5 DSCB created by os does not
correctly reflect the free space on the minidisk because os expects it
to be a full pack. In CMS, allocation occurs whenever data spaces or
unique data sets are defined, and space is released whenever data
spaces, catalogs, and unique data sets are deleted. ISAM INTERFACE PROGRAM (lIP) CMS does not
program that
method) data
sets.
support the VSAM ISAM Interface Program (lIP). Thus, any
creates and accesses ISAM (indexed sequential access
sets cannot be used to access VSAM key sequential data
There is one exception to this restriction. If you have (1) os PL/I programs that have files declared as ENV(INDEIED) and (2) if the library
routines detect that the data set being accessed is a VSAM data set,
your programs will execute VSAM I/O requests.
32 IBM VM/370 Planning and System Generation Guide
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