HCD - Hardware Configuration Definition

Enhanced Definition

Hardware Configuration Definition (HCD) is a z/OS component used to define, activate, and manage the hardware configuration of an IBM mainframe system or sysplex. It provides an interactive interface, typically via ISPF panels, to create and maintain the Input/Output Definition File (IODF), which describes the physical and logical I/O configuration. HCD ensures the operating system correctly recognizes and utilizes attached hardware resources like channels, control units, and devices.

Key Characteristics

- Integrated z/OS Component: HCD is an integral part of the z/OS operating system, not a separate product, providing core system configuration capabilities.
- IODF Management: It is the primary tool for creating, modifying, and validating IODFs, which are the central repositories for all hardware configuration data.
- Interactive Interface: HCD offers a user-friendly ISPF-based interface, allowing system programmers to define complex hardware configurations through guided menus and panels.
- Dynamic I/O Configuration: Supports dynamic activation of hardware changes, enabling modifications to the I/O configuration without requiring a full system IPL (Initial Program Load).
- Logical-to-Physical Mapping: Defines the mapping between logical device addresses (e.g., device numbers) and their corresponding physical hardware components (channels, control units, physical devices).
- Sysplex-Aware: Can manage and activate hardware configurations across multiple LPARs within a sysplex, ensuring consistent and coordinated I/O definitions.

Use Cases

- New Hardware Installation: Defining and integrating new hardware components such as disk arrays, tape libraries, network adapters (OSA), or FICON directors into the z/OS environment.
- Hardware Upgrades and Replacements: Updating the system's configuration when existing hardware is upgraded, replaced, or reconfigured (e.g., changing channel paths, control unit types).
- Configuration Changes: Modifying existing I/O definitions, such as adding or removing devices, changing device characteristics, or re-routing channel paths to optimize performance or availability.
- Disaster Recovery Planning: Establishing and maintaining alternate hardware configurations for disaster recovery sites, ensuring that recovery systems can recognize and utilize the necessary I/O resources.
- Dynamic I/O Activation: Activating minor or non-disruptive hardware changes (e.g., bringing a new disk online) without requiring a system outage, leveraging HCD's dynamic capabilities.

Related Concepts

HCD is fundamental to z/OS operations, working closely with IODFs, which it creates and manages. The active IODF is referenced by the LOADxx member in PARMLIB during an IPL to establish the initial hardware configuration. It defines the channels, control units, and devices that LPARs and the entire sysplex can access, directly impacting the availability and performance of applications running on z/OS, including CICS, DB2, and IMS.

Best Practices:

Version Control for IODFs: Treat Work IODFs as critical configuration assets and implement strict version control and change management processes for them.
Thorough Testing: Always test new or significantly modified IODFs in a non-production environment (e.g., a test LPAR) before activating them in production.
Utilize Dynamic I/O: Leverage HCD's dynamic I/O capabilities to minimize downtime for hardware changes, but understand the limitations and when an IPL might still be necessary.
Documentation: Maintain comprehensive documentation of all hardware configurations, IODF versions, and the rationale behind specific HCD definitions.
Backup and Recovery: Regularly back up IODFs and ensure a robust recovery strategy is in place for these critical configuration files.