zFS - z/OS File System

Enhanced Definition

zFS (z/OS File System) is a native, kernel-based hierarchical file system for z/OS that provides a UNIX-like file system interface and POSIX compliance. It is the strategic successor to HFS (Hierarchical File System) and is essential for supporting z/OS UNIX System Services (USS) applications and open systems workloads on the mainframe. zFS aggregates are stored within VSAM Linear Data Sets (LDS).

Key Characteristics

- Hierarchical Structure: Organizes files and directories in a tree-like structure, similar to UNIX or Windows file systems.
- POSIX Compliant: Adheres to POSIX standards, enabling the execution of UNIX applications and scripts directly on z/OS.
- VSAM LDS Based: zFS aggregates, which contain one or more zFS file systems, are allocated as VSAM Linear Data Sets, leveraging VSAM's robust data management.
- Kernel Integrated: Fully integrated into the z/OS kernel, providing efficient and direct access to file system data.
- Multi-File System Support: A single zFS aggregate can host multiple distinct zFS file systems, each mountable independently.
- Improved Performance and Scalability: Offers significant performance and scalability enhancements over its predecessor, HFS, particularly for large numbers of files and directories.

Use Cases

- Hosting USS Applications: Storing executables, libraries, and data for applications running under z/OS UNIX System Services, such as Java, Python, Node.js, and OpenSSH.
- Web and Application Servers: Providing file storage for web servers (e.g., Apache HTTP Server for z/OS) and application servers (e.g., WebSphere Application Server for z/OS).
- Open Source Tools: Managing and storing files for various open-source tools and utilities ported to z/OS, including Git, Perl, and REXX scripts for USS.
- Configuration Management: Storing configuration files for z/OS components and applications that rely on the USS environment.
- Cross-Platform Data Exchange: Facilitating data exchange and sharing with distributed systems through network file sharing protocols supported by USS.

Related Concepts

zFS is foundational to z/OS UNIX System Services (USS), providing the essential hierarchical file system structure and POSIX compliance required for UNIX applications to run on z/OS. It is the strategic replacement for the older HFS (Hierarchical File System), offering superior performance and manageability. zFS aggregates are built upon VSAM Linear Data Sets (LDS), which are managed by the z/OS system, demonstrating its reliance on core z/OS data management facilities. The OMVS kernel component manages the interaction between zFS file systems and USS processes.

Best Practices:

Monitor Space Utilization: Regularly monitor zFS aggregate and file system free space to prevent outages and ensure optimal performance.
Separate Critical File Systems: Isolate critical zFS file systems (e.g., /usr/lpp/java, /var) into their own zFS aggregates for better performance, recoverability, and easier management.
Implement Robust Backup and Recovery: Utilize DFSMShsm, ADSM/TSM, or other backup solutions to ensure timely and reliable backup and recovery of zFS aggregates.
Tune Kernel Parameters: Adjust zFS kernel parameters (e.g., cache sizes, buffer pools) based on workload characteristics and performance monitoring to optimize throughput and response times.
Secure File System Permissions: Enforce strict UNIX file permissions and ACLs (Access Control Lists) to control access to zFS files and directories, aligning with security policies.
Leverage Read-Only Mounts: Mount static or critical zFS file systems (e.g., product installation directories) as read-only where appropriate to enhance data integrity and security.