Concurrent Copy

Enhanced Definition

Concurrent Copy is a z/OS storage management feature that allows a consistent point-in-time copy of data to be created while applications continue to access and update the original data without interruption. It leverages hardware-assisted capabilities, primarily `FlashCopy`, to minimize application downtime during backup or replication operations. Concurrent Copy is a feature primarily provided by DFSMSdss (Data Facility Storage Management Subsystem data set services) on IBM z/OS systems that enables the creation of a consistent point-in-time copy of data sets or entire volumes while applications continue to update the source data. Its main purpose is to minimize application downtime during critical backup, recovery, or migration operations.

Key Characteristics

- Zero Application Downtime: Applications can continue read/write operations on the source data during the entire copy process, ensuring high availability.
- Point-in-Time Consistency: It captures a logically consistent image of the data at a specific moment, crucial for transactional systems like DB2 or IMS.
- Hardware-Assisted: Relies on advanced storage controller features, such as IBM FlashCopy on DS8000 series storage, for rapid data duplication.
- Software Integration: Typically managed by DFSMSdss (Data Facility Storage Management Subsystem data set services) or ADSM/TSM (IBM Spectrum Protect).
- Volume or Data Set Level: Can operate on entire DASD volumes or specific data sets, providing flexibility for different backup strategies.
- Reduced Backup Windows: Eliminates the need for extended application quiesce periods, significantly shortening backup windows for critical systems.

Use Cases

- Online Backups: Creating consistent backups of production DB2 databases, IMS databases, or VSAM files without taking applications offline.
- Disaster Recovery Preparation: Generating consistent copies of critical data for offsite storage or replication to a disaster recovery site.
- Test/Development Environment Refresh: Quickly provisioning consistent copies of production data to non-production environments for testing, development, or quality assurance.
- Data Migration: Facilitating the migration of data between storage subsystems or volumes with minimal impact on application availability.
- Auditing and Reporting: Creating a snapshot of data for complex reports or audits that require a consistent data set without impacting transactional performance.

Related Concepts

Concurrent Copy is fundamentally built upon the hardware capabilities of FlashCopy, which creates an instantaneous copy of a volume or data set. DFSMSdss provides the software interface and management for invoking Concurrent Copy operations, often in conjunction with ADSM/TSM for backup and recovery policies. It is a vital component of a robust Business Continuity and Disaster Recovery strategy, enabling the creation of consistent recovery points for critical DB2, IMS, and VSAM data, contrasting with traditional methods that require applications to be quiesced or offline.

Best Practices:

Coordinate with Database Utilities: For DB2 or IMS, ensure Concurrent Copy operations are coordinated with database recovery utilities (e.g., DB2 RECOVER utility with COPY YES option) to maintain log consistency and enable point-in-time recovery.
Monitor Storage Resources: Ensure sufficient FlashCopy resources (e.g., target volumes, space-efficient FlashCopy pools) are available on the storage subsystem to avoid failures or performance degradation.
Regularly Test Recovery: Periodically test the recovery process using the Concurrent Copy images to validate data integrity and ensure recovery procedures are effective.
Understand Application Consistency: For non-database applications, ensure that the application's I/O is momentarily suspended or flushed to disk before the FlashCopy is taken to guarantee application-level consistency.
Leverage Automation: Automate Concurrent Copy operations using JCL and DFSMSdss control statements or TSM policies to ensure consistent execution and reduce manual errors.