Overview of z/OS Data Set File System

With z/OS Data Set File System (DSFS), z/OS® UNIX applications can access data sets by presenting the data sets as a tree-structured file system that is mounted at mount point /dsfs in the z/OS UNIX file system tree. A utility file system is used by DSFS to contain POSIX information about the data sets accessed by applications to assist in the presentation of data sets as a tree in the z/OS UNIX file system space.

Colony address space

DSFS runs as a physical file system (PFS) in a z/OS UNIX colony address space. It cannot run inside the z/OS UNIX address space. For more information about colony address spaces, see Running a physical file system in a colony address space in z/OS UNIX System Services Planning.

Supported data sets

DSFS supports the following data sets:
  • Fixed and variable-length record physical sequential data sets (PS)
  • Partitioned data sets (PDS)
  • Partitioned data set extended (PDSE)
DSFS does not support variable-spanned record data sets. It does not allow access to encrypted data sets unless the utility file system data set is also encrypted. DSFS supports only cataloged data sets. If the catalog contains more than one entry for a data set, DSFS will use the entry in the master catalog. It does not support aliases, VSAM data sets, or migrated data sets. Because those data sets are not shown in the directory tree, they will not be accessible to DSFS users.

Case sensitivity

DSFS is a case-insensitive physical file system. File names and directory names are returned in lowercase. It also converts any input name to lowercase and stores it as lowercase. When DSFS interacts with the z/OS system through DFSMS, it converts the names to uppercase.

When specifying names in the DSFS tree, use lowercase. If uppercase names are specified, unpredictable results can occur. For example, an ls command with a wildcard and uppercase characters will result in failed pattern matching.

Security

DSFS runs with the requesting application user credentials for all access to data sets. For those cases where DSFS might cache data to reduce access calls to data sets, DSFS will make specific SAF calls to verify that the user has the required authority for all accesses to cached data. DSFS does not use z/OS UNIX security protocols.

Utility file system

DSFS requires the administrator to define a linear data set by using the DEFINE CLUSTER command with the ZFS keyword to define a utility file system. This file system is used to store the directory tree that is used to represent the accessed data sets as a file system tree and will cache POSIX byte-stream representations of the data sets that are being read and written by applications. Each system in a shared file system will use its own utility file system for its processing. If the user defines a key label for the data set, then DSFS encrypts the data that it stores in the utility file system. DSFS also allows an option for transparent data compression of the files that it stores in its utility file system.

Parameters file (IDFFSPRM)

DSFS allows specification of a parameters file or allows for parmlib search to be used to specify parameters that control DSFS behavior. Many of these parameters can also be dynamically modified while DSFS is running.

The dsadm commands

DSFS provides commands that can query utility file system usage or statistics for a particular file or directory. Commands are also provided to enable the administrator to configure and monitor DSFS.