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Corrupt

Enhanced Definition

In the mainframe context, **corrupt** refers to data, a file, a dataset, a program, or a system component that has become damaged, inconsistent, or invalid, rendering it unusable or causing abnormal system behavior. This state typically results from hardware failures, software defects, I/O errors, or improper system operations, leading to a loss of data integrity or system functionality.

Key Characteristics

- Data Inconsistency: Data no longer adheres to its defined structure or expected values, leading to logical errors in applications or incorrect processing.
- Unreadable or Unusable: Files or datasets may become unreadable by standard access methods (e.g., VSAM, QSAM) or cause programs to abend when attempting to process them.
- System Instability: Corruption in critical system datasets (e.g., VTOC, VVDS, catalogs) can lead to system crashes, IPL failures, or widespread application outages.
- Error Messages and Abends: Often detected through specific error codes (e.g., IEC messages for I/O errors, ABEND codes like 0C4, 0C7, D37, B37) issued by the operating system or application programs.
- Loss of Data Integrity: The primary consequence is that the data can no longer be trusted, potentially leading to incorrect business decisions or regulatory non-compliance.

Use Cases

- VSAM KSDS Corruption: A hardware error or system crash during a write operation might leave a VSAM KSDS (Key-Sequenced Data Set) with a damaged index or control interval, making records inaccessible or causing ABENDs like IDCAMS 0C7 when accessed.
- DB2 Table Space Corruption: A DB2 table space might become corrupt due to a disk failure or a DB2 subsystem error, leading to SQLCODE -904 or DSNT500I messages, preventing access to the data until recovery.
- z/OS Catalog Corruption: Damage to a z/OS master catalog or user catalog can prevent the system from locating datasets, causing JCL jobs to fail with IEF212I or IEC104I errors, impacting multiple applications.
- Load Module Corruption: A program load module in a PDS or PDSE library might become corrupt, causing ABENDs (e.g., 0C1, 0C4) when the program is loaded and executed, indicating invalid instructions or data areas.