Data Facility Storage Management Subsystem (MVS)

Data Facility Storage Management Subsystem (DFSMS) is a central component of IBM's flagship operating system z/OS. It includes access methods, utilities and program management functions. Data Facility Storage Management Subsystem is also a collective name for a collection of several products, all but two of which are included in the DFSMS/MVS product.

History
In 1972 IBM announced the first release of the OS/VS2 operating system for the IBM System 370 systems; that release later was known as Single Virtual Storage (SVS). In 1974 IBM announced release 2.0; that release and all subsequent releases became known as Multiple Virtual Storage (MVS). All releases of OS/VS2 were available to no charge because the software cost was bundled with the hardware cost. OS/VS2 Release 3.8 was the last free release of MVS.

In the late seventies and early eighties IBM announced:


 * 5740-XE1 MVS/System Extensions (MVS/SE)
 * MVS/SE improves the performance and RAS of OS/VS2 (MVS)


 * 5740-AM6 Data Facility Device Support (DFDS) for OS/VS1
 * 5740-AM7 Data Facility Device Support (DFDS) for MVS
 * DFDS supports an indexed VTOC, and with the proper PTF supports the Speed Matching Buffer on the IBM 3880.


 * 5740-XYQ Data Facility Extended Function (DFEF)
 * DFEF offers a new type of VSAM catalog, but had reliability problems that were only resolved in DFP.


 * 5740-AM3 Sequential Access Method Extended (SAM-E)
 * SAM-E improves the performance of BPAM, BSAM and QSAM on direct access storage devices.


 * 5740-AM8 Access Method Services Cryptographic Option


 * 5748-UT2 Offline 3800 Utility

In June 1980, IBM announced MVS/System Product (MVS/SP) as a replacement for MVS/SE.

On October 21, 1981, IBM announced new Kxx models of the 3081, supporting a new architecture known as System/370 Extended Architecture (370-XA). IBM also announced MVS/Extended Architecture (MVS/XA), consisting of MVS/SP Version 2 and a corequisite new product, Data Facility Product (DFP), 5665-284, replacing five of the products listed above, the linkage editor and the loader.

On May 17, 1983, IBM announced MVS/370 Data Facility Product (MVS/370 DFP), 5665-295, for MVS/SP Version 1 Release 3, replacing the same five programs as DFP for MVS/XA.

On February 5, 1985, IBM announced MVS/XA Data Facility Product (MVS/XA DFP) Version 2, 5655-XA2, as a replacement for MVS/XA Data Facility Product Version 1, 5665-284. DFP replaced BDAM, BPAM, BSAM, ISAM, QSAM and VSAM.

On February 15, 1988 IBM announced MVS/System Product Version 3 (MVS/ESA), it also announced MVS/Data Facility Product Version 3 (MVS/DFP), 5665-XA3; MVS/SP V3 required either MVS/XA Data Facility Product Version 2, 5655-XA2, or Version 3. More recent releases were corequisites for MVS/ESA SP Version 4 and MVS/ESA SP Version 5.

On April 19, 1988, IBM announced the umbrella term Data Facility Storage Management Subsystem for facilities provided by the programs
 * IBM MVS/Data Facility Product (MVS/DFP) Version 3 Release 1.0
 * IBM Data Facility Data Set Services (DFDSS) Version 2 Release 4.0
 * IBM Data Facility Hierarchical Storage Manager (DFHSM) Version 2 Release 4.0
 * IBM Resource Access Control Facility (RACF) Release 8.1
 * IBM Data Facility Sort (DFSORT) Release 10.0

In addition to replacing part of the device support in the base MVS/SP, DFP replaces the Linkage Editor and several utility programs and service aids.

DFP is no longer available as a separate product, but has become part of Data Facility Storage Management Subsystem, under the name DFSMSdfp.

On May 19, 1992, IBM announced DFSMS/MVS, 5695-DF1, replacing MVS/Data Facility Product (MVS/DFP) Version 3, 5665-XA3, Data Facility Hierarchical Storage Manager (DFHSM) Version 2, 5665-329 and Data Facility Data Set Services (DFDSS) Version 2, 5665-327. DFSMS/MVS also replaced utilities and service aids. DSDSS and DFHSM became optional chargeable features of DFSMS; DFSORT and RACF remained separate products. While DFSMS/MVS Release 1 still included ISAM, IBM eventually dropped it, but continued to support the ISAM compatibility interface to VSAM. DFSMS/MVS R1 included the optional Removeable Media Manager (DFSMSrmm), which supports both manual tape libraries and the 3495 Tape Library Dataserver.

On March 1, 1994, IBM announced DFSMS/MVS Release 2.

On March 1, 1994, IBM announced DFSMS/MVS Release 3.

On March 1, 1994, IBM announced DFSMS/MVS Release 4.

On March 1, 1994, IBM announced DFSMS/MVS Release 5.

Components
This section describes features of DFSMS from the perspective of z/OS; it does not distinguish between features added by, e.g., DFDS, and features added in the latest release of z/OS.

DFSMSdss
DFSMSdss is a chargeable feature of DFSMS that can dump and restore selected data sets and selected volumes based on specifications in control statements. It is also referred to in documentation as a data mover. DSS replaces the older DASDR and the dump/restore facilities of IEHDASDR, although the dump formats are not compatible.

DFSMSdfp
DFSMSdfp replaces the older direct, index and sequential access methods, the utilities and service aids, the linkage editor, the loader and program fetch. It is the component to which new device support code is added. DFSMSdfp adds a number of loosely related facilities.

Indexed VTOC
The VTOC structure inherited from OS/360 uses records with 44 byte keys, and a sequential search using a Search Key Equal/TIC *-8 loop. The VTOC Index (VTOCIX) is an optional data set that indexes Data Set Control Blocks (DSCBs) and allows a faster search.

ICF catalog
The Improved Catalog Facility (ICF) replaces the OS/360 Control Volume (CVOL) and the VSAM catalog with a more resilient catalog structure.

PDSE
Partitoned Data Set Extended (PDSE) is a new type of dataset that resolves several issues with the old PDS organization but that can be read and written by existing BPAM, BSAM and QSAM code.

System Managed Storage
System Managed Storage (SMS) is a set of facilities for controlling the placement, migration and retention of datasets on direct access storage devices that is more flexible than older methods, e.g., VOL=SER specifications in JCL. Prior to SMS, the installations defined unit names during system generation, and two pools of DASD volumes, called PUBLIC and STORAGE, in a member of the system parameter library. In addition, users had to explicitly define characteristics of new datasets.

With SMS, an installation can define and update several types of lists, described by IBM as
 * Data Class
 * Data definition parameters


 * Storage Class
 * Availability and accessibility requirements


 * Management Class
 * Data migration, backup, and retention attributes


 * Storage Group
 * List of storage volumes with common properties


 * Aggregate Group
 * Backup or recovery of all data sets in a group in a single operation

The installation can also define automatic class selection (ACS) rules that can test, e.g., data set name, and select list names based on installation policies and user requests. A common scenario is for the installation to write a storage group ACS routine to ignore any UNIT parameter and to select the storage group, and to write a DATACLASS ACS rule to assign a dataclass that has default DCB parameters, with both making decisions based on the data set name.
 * Copy Pool

When SMS is active, several new parameters are available in dynamic allocation and the DD JCL statement, e.g., DSNTYPE.

The Binder
The Binder is a program similar to the linkage editor that can also manage program objects on a PDSE library.

Remote copy and mirroring
DFSMSdfp provides facilities for using several different protocols to duplicate or mirror DASD volumes to a remote location.

OAM
Object Access Method (OAM) maintains a library of unstructured objects. Such objects are sometimes referred to as BLOBs.

DFSORT
DFSORT is a sort/merge utility that is part of the DFSMS family but not part of the DFSMS/MVS product.

DFSMShsm
DFSMShsm, originally Hierarchical Storage Manager (HSM), 5740-XRB, and later Data Facility Hierarchical Storage Manager Version 2 (DFHSM), 5665-329, before becoming an optional component of DFSMS, is a utility for archiving and retrieving datasets. It migrates data from faster storage to less expensive storage, either based on time stamps or explicit requests. It uses DFSMSdss as a data mover.

RACF
RACF is a security program that is part of the DFSMS family but not part of the DFSMS/MVS product. It includes an API called SAF that allows applications to do authentication and to check access privileges, and also includes an interface to LDAP.

DFSMSrmm
The Removable Media Manager (DFSMSrmm) controls libraries of tapes, whether manually mounted on tape drive or stored in an automated tape library.