Erase
In the mainframe context, "erase" primarily refers to the process of deleting or removing data, datasets, or storage objects from a storage volume (DASD or tape) or within a database. This action makes the data inaccessible to applications and users, and typically frees up the associated storage space for reuse by the system. In the context of IBM z/OS, "erase" primarily refers to the process of removing data from storage. This can range from a logical deletion, where data is simply marked as no longer valid and its space made available, to a secure physical overwrite that renders the data unrecoverable.
Key Characteristics
-
- Logical Deletion: Often, an erase operation is a logical deletion, where the system marks data blocks as available but does not immediately overwrite the actual data. The data might physically persist until new data occupies those blocks.
- Physical Deletion (Secure Erase): For sensitive data, a secure erase involves overwriting the data multiple times with specific patterns (e.g., zeros, ones, random data) to prevent forensic recovery.
- Scope: Erase operations can apply to entire datasets (e.g., sequential, PDS/PDSE, VSAM), individual records within a dataset or database, or even entire storage volumes.
- Resource Release: Successfully erasing data releases the storage space back to the operating system or storage management subsystem for allocation to new datasets or applications.
- Irreversibility: Once data is erased, especially physically, its recovery can be difficult or impossible without prior backups or specialized data recovery tools.
- System-Managed: Erase operations are typically managed by the z/OS operating system, storage management subsystems (like DFSMS), or database management systems (DB2, IMS).
Use Cases
-
- Dataset Management: Deleting temporary datasets (
DISP=(NEW,DELETE)) or obsolete permanent datasets (DISP=(OLD,DELETE)) via JCL to reclaim DASD space. - Database Record Removal: Deleting specific records from a DB2 table using
DELETESQL statements or removing segments from an IMS database when they are no longer needed. - Tape Scratching: Marking tape volumes as
SCRATCH(available for reuse) within a tape management system (e.g., DFSMSrmm) after their retention period expires, effectively erasing their logical content. - Secure Data Disposal: Using utilities like
ICKDSFor third-party products to securely overwrite sensitive data on DASD volumes before decommissioning or repurposing. - VSAM Cluster Deletion: Removing an entire VSAM KSDS, ESDS, or RRDS cluster using the
IDCAMS DELETEcommand, which also deletes its associated data and index components.
- Dataset Management: Deleting temporary datasets (
Related Concepts
Erase is fundamental to storage management in z/OS, closely tied to JCL (via the DISP parameter), IDCAMS for VSAM and non-VSAM datasets, and DFSMS for automated storage and data lifecycle management. It complements backup and recovery strategies by defining when data is no longer needed and can be safely removed. Furthermore, it intersects with data security through secure erase techniques to prevent unauthorized data retrieval and ensure compliance.
- Verify Before Erase: Always ensure that the data or dataset targeted for erasure is indeed obsolete and no longer required by any application, user, or regulatory requirement.
- Implement Retention Policies: Establish and adhere to strict data retention policies to automate the identification and erasure of expired data, especially for tape volumes and archive datasets.
- Secure Erase for Sensitive Data: For data containing Personally Identifiable Information (PII) or other sensitive information, utilize secure erase utilities to overwrite data multiple times to prevent recovery.
- Backup Critical Data: Before performing any major erase operation on permanent datasets, ensure that a recent, valid backup exists, especially if there is any doubt about its necessity.
- Monitor Storage Utilization: Regularly monitor DASD and tape storage utilization to identify opportunities for erasing obsolete data and reclaiming valuable system resources.