IFS - Installable File System
An Installable File System (IFS) in z/OS refers to a type of file system that can be dynamically mounted and integrated into the z/OS UNIX System Services (USS) file hierarchy. Its primary purpose is to provide access to data residing on various storage types or managed by different file system implementations, making them appear as native USS files and directories.
Key Characteristics
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- Dynamic Mounting: IFS instances can be mounted and unmounted on the fly using the
MOUNTandUNMOUNTcommands, without requiring an IPL (Initial Program Load). - Integration with USS: Once mounted, an IFS becomes an integral part of the z/OS UNIX file system tree, accessible via standard UNIX commands, APIs, and applications.
- Diverse Implementations: Common IFS implementations include zFS (z/OS File System), HFS (Hierarchical File System - an older predecessor to zFS), and NFS (Network File System) client capabilities.
- Unified View: It provides a unified, hierarchical view of potentially diverse data sources, abstracting the underlying storage and management mechanisms.
- Kernel Interface: IFS implementations interact with the z/OS kernel's file system interface to manage file operations, I/O, and metadata.
- Security Integration: Access to files and directories within an IFS is governed by z/OS security mechanisms like RACF, ACF2, or Top Secret, enforcing permissions based on UNIX user IDs (UIDs) and group IDs (GIDs).
- Dynamic Mounting: IFS instances can be mounted and unmounted on the fly using the
Use Cases
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- Native z/OS UNIX Storage: zFS is the primary and recommended IFS for storing all native z/OS UNIX files, including application binaries, configuration files, scripts, and user data.
- Network File Sharing: Mounting remote NFS shares from other UNIX, Linux, or Windows systems onto z/OS USS, allowing z/OS applications to access distributed data seamlessly.
- Application Development: Providing a shared, version-controlled file system for COBOL, C/C++, Java, and other application source code and build artifacts within the USS environment.
- Middleware Deployment: Hosting middleware components like WebSphere Application Server, Apache HTTP Server, or other open-source tools that require a UNIX-like file system structure.
Related Concepts
IFS is a foundational component of z/OS UNIX System Services (USS), providing the actual file system structure and data storage mechanism that USS applications interact with. zFS (z/OS File System) is the strategic and most commonly used IFS implementation for native z/OS UNIX data, offering significant performance and scalability advantages over its predecessor, HFS (Hierarchical File System). When z/OS acts as an NFS client, it uses an IFS to mount and access remote network file systems, integrating them into its local USS hierarchy. Each IFS instance is attached to a specific mount point (a directory) within the existing USS file system tree.
- Prioritize zFS: Always create new z/OS UNIX file systems using zFS rather than HFS due to its superior performance, recoverability, and scalability features.
- Proper Sizing and Allocation: Allocate sufficient space for zFS aggregates (VSAM linear data sets) to prevent out-of-space conditions, and monitor free space regularly.
- Regular Backups: Implement robust backup and recovery procedures for all critical IFS data, especially zFS aggregates, using tools like DFSMSdss or other backup utilities.
- Security Configuration: Define appropriate RACF (or equivalent) profiles for IFS aggregates and mount points, ensuring proper UIDs, GIDs, and permissions are assigned to control access effectively.
- Performance Monitoring: Monitor IFS performance metrics (e.g., I/O rates, CPU usage, cache hit ratios for zFS) to identify and resolve bottlenecks.