Data Facility Storage Management Subsystem (MVS)
| Company type | Software suite |
|---|---|
| Industry | Computer software |
| Founded | 1988 |
| Founder | IBM |
| Headquarters | Armonk , United States |
| Products | DFSMS/MVS, DFSMSdfp, DFSMSdss, DFSMShsm, DFSORT, RACF, DFSMSrmm |
| Owner | IBM |
Data Facility Storage Management Subsystem (DFSMS) represents a fundamental element of IBM's premier operating system z/OS. It integrates access methods, utility programs, and software management capabilities. The designation also collectively identifies multiple products, primarily encompassed within DFSMS/MVS.
History
IBM introduced OS/VS2 for System/370 in 1972, which later became known as Single Virtual Storage (SVS). By 1974, the release of version 2.0 brought forth Multiple Virtual Storage (MVS). These OS/VS2 versions were distributed at no cost alongside hardware; OS/VS2 Release 3.8 marked the final free iteration of MVS.
Throughout the late 1970s and early 1980s, IBM launched several significant offerings, including:
- 5740-XE1 MVS/System Extensions (MVS/SE) – designed to boost performance and dependability of OS/VS2 (MVS)
- 5740-AM6 and AM7 Data Facility Device Support (DFDS) for OS/VS1 and MVS – providing support for indexed VTOC and Speed Matching Buffer on IBM 3880
- 5740-XYQ Data Facility Extended Function (DFEF) – featuring a novel VSAM catalog, initially plagued by reliability challenges
- 5740-AM3 Sequential Access Method Extended (SAM-E) – enhancing BPAM, BSAM, and QSAM efficiency on direct access storage devices
- 5740-AM8 Access Method Services Cryptographic Option
- 5748-UT2 Offline 3800 Utility
In June 1980, IBM introduced MVS/System Product (MVS/SP), which succeeded MVS/SE.
On October 21, 1981, IBM announced the launch of new 3081 Kxx models equipped with System/370 Extended Architecture (370-XA), accompanied by MVS/Extended Architecture (MVS/XA) Version 2 and the Data Facility Product (DFP), which replaced five prior products including the linkage editor and loader.
By May 1983, MVS/370 DFP updated these replacements to support MVS/SP Version 1 Release 3. In February 1985, MVS/XA DFP Version 2 further superseded BDAM, BPAM, BSAM, ISAM, QSAM, and VSAM.
On February 15, 1988, IBM released MVS/System Product Version 3 (MVS/ESA) alongside MVS/Data Facility Product Version 3 (MVS/DFP), which became essential companions for future MVS/ESA iterations.
April 19, 1988 saw the introduction of the collective term Data Facility Storage Management Subsystem, encompassing:
- IBM MVS/Data Facility Product 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
DFP also replaced device support modules within base MVS/SP as well as the Linkage Editor and various utility programs. Since then, DFP has been incorporated into DFSMS under the name DFSMSdfp.
On May 19, 1992, IBM unveiled DFSMS/MVS as a successor to MVS/Data Facility Product Version 3, DFHSM Version 2, and DFDSS Version 2. This new suite integrated additional utilities; while DFDSS and DFHSM became optional chargeable components, DFSORT and RACF continued as standalone products. Although ISAM was eventually discontinued, compatibility was preserved through VSAM interfaces. The initial release of DFSMS/MVS included the optional Removable Media Manager (DFSMSrmm), which facilitated manual tape libraries along with support for the IBM 3495 Tape Library Dataserver.
Subsequent DFSMS/MVS versions were released on the following dates:
- March 1, 1994 – DFSMS/MVS Release 2
- May 30, 1995 – DFSMS/MVS Release 3
- September 10, 1996 – DFSMS/MVS Release 4
- June 9, 1997 – DFSMS/MVS Release 5
Components
This segment presents an overview of DFSMS capabilities from the z/OS viewpoint, without differentiating between features introduced by DFDS or recent z/OS versions.
DFSMSdss
DFSMSdss is a billable DFSMS component designed for dumping and restoring chosen data sets and volumes through control statements. Often referred to as a data mover, it replaces legacy dump/restore utilities such as DASDR and IEHDASDR, although the dump formats it uses are distinct.
DFSMSdfp
Replacing older access methods, utilities, linkage editors, loaders, and program fetch processes, DFSMSdfp serves as the foundation for new device support code. It encompasses several key functionalities:
Indexed VTOC
The VTOC Index (VTOCIX) is an optional data set that provides an index of Data Set Control Blocks (DSCBs), accelerating searches beyond the original sequential 44-byte key approach inherited from OS/360.
ICF catalog
The Improved Catalog Facility (ICF) supersedes the OS/360 Control Volume (CVOL) and VSAM catalogs by offering a more robust and reliable structure.
PDSE
Partitioned Data Set Extended (PDSE) addresses limitations found in the older PDS format while maintaining compatibility with existing BPAM, BSAM, and QSAM interfaces.
System Managed Storage
System Managed Storage (SMS) provides enhanced flexibility in managing dataset allocation, migration, and retention on direct access storage devices, improving upon previous VOL=SER JCL conventions. Earlier implementations required defining device names during system generation and managing two DASD volume pools—PUBLIC and STORAGE—via system parameter libraries, with explicit dataset attribute specifications.
With SMS in place, installations configure and maintain lists such as:
- Data Class – Parameters defining data characteristics
- Storage Class – Criteria for availability and accessibility
- Management Class – Policies governing migration, backup, and retention
- Storage Group – Sets of storage volumes sharing common traits
- Aggregate Group – Facilitates backup and recovery of all group datasets as a single unit
- Copy Pool
Automatic class selection (ACS) rules analyze dataset names to assign appropriate classes based on established policies. It is common to override UNIT parameters using storage group ACS routines while assigning default DCB parameters through dataclass ACS rules.
When SMS is active, dynamic allocation and DD JCL statements accept new parameters including DSNTYPE.
The Binder
The Binder functions similarly to a linkage editor by managing program objects stored within PDSE libraries.
Remote copy and mirroring
DFSMSdfp supports various protocols that enable duplication or mirroring of DASD volumes across remote sites, thereby enhancing data availability and disaster recovery capabilities.
OAM
Object Access Method (OAM) administers libraries containing unstructured objects—commonly known as BLOBs—providing adaptable storage solutions.
DFSORT
DFSORT is a high-efficiency sort/merge utility affiliated with the DFSMS family but operates independently from DFSMS/MVS itself.
DFSMShsm
DFSMShsm, known as the Hierarchical Storage Manager, facilitates automated data archiving by transferring datasets from high-speed storage to more economical options according to predefined policies or specific user commands. It relies on DFSMSdss to perform the actual data movement.
RACF
RACF, although affiliated with the DFSMS suite, operates independently from DFSMS/MVS and delivers security management services. It features the SAF API for handling authentication and access control tasks, and supports integration with LDAP directories.
DFSMSrmm
The Removable Media Manager (DFSMSrmm) is responsible for controlling tape library operations, including coordination of manual tape mounts as well as automated tape library management systems.