FlashCopy - Fast disk copy
FlashCopy is a hardware-assisted feature of IBM storage systems, primarily the DS8000 series, that creates an instantaneous, point-in-time copy of a source volume to a target volume. This operation is performed by the storage controller, offloading the host CPU and enabling rapid data replication for various mainframe use cases.
Key Characteristics
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- Instantaneous Copy: The logical copy operation completes almost instantly, regardless of the size of the source volume, as it primarily involves updating metadata pointers.
- Point-in-Time Consistency: Captures the data exactly as it exists at the moment the FlashCopy command is issued, ensuring a consistent snapshot.
- Hardware-Assisted: The entire copy process is managed by the storage subsystem, minimizing impact on z/OS host CPU and I/O resources.
- Copy-on-Write (NOCOPY mode): In
NOCOPYmode, data is only physically copied from source to target when a write operation occurs on either the source or target volume to a track that has not yet been copied. This saves space and time. - Full Copy (COPY mode): In
COPYmode, all data tracks are physically copied from the source to the target volume in the background, making the target an independent copy. - Incremental FlashCopy: Allows subsequent FlashCopy operations to only copy tracks that have changed since the previous FlashCopy, improving efficiency for recurring backups.
- Read/Write Access: Both the source and target volumes remain fully accessible for read and write operations immediately after the FlashCopy command completes.
Use Cases
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- Rapid Backups: Creating consistent backups of critical production databases (e.g., DB2, IMS) or file systems (e.g., zFS) with minimal application downtime, often coordinated with application
QUIESCEcommands. - Development and Test Environments: Quickly provisioning fresh, production-like data for development, testing, and quality assurance environments, significantly reducing setup time.
- Disaster Recovery Testing: Facilitating non-disruptive disaster recovery drills by creating copies of production data for testing recovery procedures without impacting live systems.
- Data Migration and Reorganization: Assisting in migrating data between different storage tiers, performing volume reorganizations, or creating copies for data transformation processes.
- Application Consistency: Used in conjunction with z/OS utilities like
DFSMSdssorADRDSSUto manage FlashCopy operations at the dataset level, ensuring data integrity for specific applications.
- Rapid Backups: Creating consistent backups of critical production databases (e.g., DB2, IMS) or file systems (e.g., zFS) with minimal application downtime, often coordinated with application
Related Concepts
FlashCopy is a fundamental component of IBM's storage management strategy for z/OS, often integrated with DFSMSdss or ADRDSSU for data set level operations. It forms the basis for advanced High Availability and Disaster Recovery solutions like GDPS when combined with remote replication technologies such as Metro Mirror or Global Mirror. For data consistency, it is frequently coordinated with database utilities to QUIESCE applications like DB2 or IMS before the copy operation.
- Quiesce Applications: For critical applications, always
QUIESCEthe application (e.g.,DB2 QUIESCE,IMS DBRC) or ensure a consistent state before initiating a FlashCopy to guarantee data integrity on the target volume. - Monitor Progress: Actively monitor the progress of FlashCopy operations, especially in
COPYmode, to ensure timely completion and manage storage resource utilization effectively. - Capacity Planning: Ensure adequate target volume capacity and understand the space implications of
NOCOPYversusCOPYmodes, particularly forNOCOPYwhere source and target share physical tracks. - Automate Operations: Automate FlashCopy commands through JCL, REXX, or scripting with
DS CLIto ensure repeatable, error-free, and scheduled execution. - Regular Testing: Periodically test the recovery and usability of data from FlashCopy targets to validate the integrity of the copies and the effectiveness of recovery procedures.