Copy methods

Advanced Image Copy Services uses the DFSMSdss cross-memory API, ADRXMAIA, to process DFSMSdss DUMP and COPY commands. These commands allow IMS HP Image Copy to use the following DFSMSdss Advanced Copy Services: Concurrent Copy, FlashCopy®, and SnapShot Copy.

If IMS database data sets reside on EMC DASD, you can request IMS HP Image Copy to use the EMC TimeFinder/Clone API instead of DFSMSdss API.

Subtopics:

FlashCopy

FlashCopy enables you to make copies of data sets, with the copies immediately available for read or write access. Subsequent updates to the original data sets are not reflected in the output data sets.

FlashCopy creates a copy of a source volume on the target volume. This copy is called a point-in-time copy. Access to the point-in-time copy of the data on the source volume is through reading the data from the target volume. The actual point-in-time data that is read from the target volume might or might not be physically stored on the target volume. As soon as a FlashCopy relationship is established, the point-in-time data is available for reading from the target volume. However, if data is written to a data set that is a target data set in a FlashCopy relationship and the updated target data set is read afterward, the data that is returned is user-updated data, and not the point-in-time source data set data. Target data sets are withdrawn from a FlashCopy relationship as soon as any application writes to these data sets. FlashCopy supports both System z®-attached (CKD) devices and Open System (FB) devices.

IMS HP Image Copy can use FlashCopy only for DASD that supports FlashCopy Version 2. With FlashCopy Version 2, restrictions on source and target volumes being in the same logical subsystem have been lifted. The target data sets can be on the same volume as the source or any other volume within the same ESS subsystem. Also, multiple source copies can be made to different target locations.

For more information about FlashCopy, see the following topics in z/OS® DFSMS Advanced Copy Services :
  • "FlashCopy"
  • "Overview of FlashCopy"

SnapShot Copy

SnapShot Copy is a feature on the RAMAC Virtual Array (RVA) device. Similar support exists for OEM devices. SnapShot Copy provides fast data replication using a combination of hardware and software services. SnapShot Copy functions only when the source and target locations reside within the same RVA subsystem. SnapShot Copy runs only when both the source data set and target data set reside on SnapShot Copy capable devices within the same storage subsystem.

Concurrent Copy

Concurrent copy of DFSMSdss is a storage subsystem extended function that provides point-in-time data consistency. The system serializes access to the data just long enough for the concurrent copy session to initialize. This serialization takes a matter of seconds. The copy is logically complete as soon as you have initialized the concurrent copy environment. At that point, concurrent copy protects the original state of the data. After logical completion, the serialization of the data set is released and the data is made available.

When DFSMSdss Concurrent Copy is used in creating image copies, the image copy process occurs in two phases: logical copy processing phase and then physical copy processing phase.
Logical copy processing
Serialization is obtained on the data sets and logical copy processing starts. This phase takes a small amount of time in relation to the total time required to create the image copy. Once the logical copy is complete, serialization of the data sets is released and the databases become available for updates.

Logical copy processing is performed for both batch image copy (IC/AIC) and concurrent image copy (CIC/ACIC) processing.

  • Any changes made to the data sets after the logical copy completes are not reflected in the image copy.
  • Even though the database data sets are serialized, database records are not committed to IMS. Therefore, the generated concurrent image copies are fuzzy image copies of the data sets.
  • When creating batch image copies, the databases can be brought back online after logical copy completes.
Physical copy processing
After the logical copy processing is complete, the physical copy processing begins. During this time, the records from the source data set are processed and the actual (physical) image copy is created. The image copy is not available until the physical copy processing completes.

EMC TimeFinder/Clone

EMC TimeFinder is a data set replication product for creating and managing point-in-time copies of data. EMC TimeFinder/Clone enables you to make copies of a set of tracks, with the copies immediately available for read or write access.

If you specify DATA_MOVER=EMCSNAP, IMS HP Image Copy uses EMC TimeFinder/Clone instead of FlashCopy or SnapShot of DFSMSdss. For more information about configuring EMC TimeFinder, see the product documentation for EMC TimeFinder.