Hierarchical File System (IBM MVS)

HFS
Developer(s)	IBM
Full name	z/OS Hierarchical File System
Introduced	1993 with DFSMS/MVS Version 1.2 for MVS/ESA
Other
Supported; operating systems	included in z/OS (until 2.5), all releases of OS/390, and MVS/ESA V5R1 and higher (optional for V4R3)

IBM's Hierarchical File System (HFS) is a POSIX-style hierarchical file system^[1] for the MVS/ESA/SP through z/OS operating systems.

IBM introduced HFS on February 9, 1993 in MVS/ESA System Product Version 4 Release 3 OpenEdition^[2]^[3] with DFSMS/MVS Version 1 Release 2^[4] for 3090 mainframes. On April 6, 1994, IBM introduced MVS/ESA System Product (MVS/ESA SP) Version 5 Release 1,^[5] which included MVS OpenEdition (MVS-OE) with HFS as a standard component. IBM continued providing HFS through z/OS 2.4 for z System mainframes.

IBM functionally stabilized HFS starting with z/OS 1.7, in 2005.^[6] The z/OS File System (zFS) was released as the higher performance successor to HFS in 1995, and IBM recommended migration from HFS to zFS. Following the release of zFS, z/OS releases included a tool, BPXWH2Z, to convert HFS to zFS.^[7]

IBM dropped the use of HFS in z/OS 2.5, in 2021.^[6]