Hard Error

Enhanced Definition

A hard error in the mainframe context refers to a permanent, unrecoverable failure of a hardware component, I/O operation, or software resource that prevents continued processing without intervention. Unlike a soft error, which might be transient or correctable, a hard error indicates a fundamental problem requiring repair, replacement, or re-configuration.

Key Characteristics

- Unrecoverable: The system cannot automatically recover from a hard error; manual intervention (e.g., operator action, hardware replacement, re-IPL) is typically required.
- Persistent: The error will recur if the same operation or resource is attempted again without addressing the underlying issue.
- Often Hardware-Related: Frequently associated with physical damage or malfunction of DASD (Direct Access Storage Device), tape drives, controllers, memory modules, or CPU components.
- Can Impact System Stability: A severe hard error can lead to ABENDs (Abnormal Ends), data corruption, or the inability to access critical system resources, potentially causing a system outage.
- Logged Extensively: z/OS extensively logs hard errors in system logs (e.g., SYSLOG, LOGREC) with detailed error codes, sense data, and diagnostic information.
- Requires Operator Intervention: Typically results in messages to the system console (e.g., IEC, IOS, ABEND codes) requiring an operator to respond or take action.

Use Cases

- I/O Device Failure: A DASD volume experiences a permanent read/write head failure, leading to IOS (Input/Output Supervisor) errors (e.g., IOS000I) whenever data is accessed from that specific track or volume.
- Memory Module Failure: A CPU experiences a hard error in a memory module, causing repeated ABENDs like 0C4 (protection exception) or 0C7 (data exception) in programs attempting to use the faulty memory.
- Channel Path Error: A physical channel path connecting a CPU to a storage controller fails permanently, preventing communication with attached DASD or tape devices, resulting in IOS errors.
- Software Resource Corruption: A critical system control block or dataset (e.g., VTOC on a DASD) becomes permanently corrupted, leading to repeated ABENDs or system instability until the resource is restored from backup.
- Tape Drive Malfunction: A tape drive experiences a permanent mechanical failure, causing IEC messages and ABENDs when JCL attempts to allocate or read/write to a tape on that drive.

Related Concepts

Hard errors are distinct from soft errors, which are transient and often correctable by the system (e.g., ECC memory correcting a single-bit flip). They are a significant cause of ABENDs (Abnormal Ends) and system outages, often necessitating IPLs (Initial Program Loads) or hardware maintenance. Diagnosis frequently involves analyzing SYSLOG, LOGREC, and dump files to pinpoint the failing component or resource, and may necessitate interaction with hardware maintenance engineers or IBM support.

Best Practices:

Proactive Monitoring: Implement robust system monitoring tools (e.g., OMEGAMON, RMF) to detect early warning signs of hardware degradation or increasing error rates before they escalate to hard errors.
Regular Backups and Recovery Plans: Maintain frequent and reliable backups of critical data and system configurations, along with well-tested disaster recovery plans, to facilitate rapid recovery in case of data loss or system impact due to a hard error.
Prompt Operator Response: Ensure system operators are well-trained to recognize and respond appropriately to hard error messages, following documented procedures for problem determination, escalation, and isolation of faulty resources.
Hardware Maintenance: Adhere to vendor-recommended hardware maintenance schedules and promptly address any reported hardware issues to prevent minor problems from escalating into critical hard errors.
Thorough Diagnostic Analysis: When a hard error occurs, thoroughly analyze SYSLOG, LOGREC, dumps, and sense data to identify the root cause, prevent recurrence, and provide accurate information to hardware support.