- COPY runs a background copy. This is the
default operation.
The COPY mode causes all tracks in the FlashCopy relationship to be physically copied from the source volume tracks to the target volume tracks. For FlashCopy V1 operations, the source tracks are copied to the target volume in the same track locations as the source tracks. For FlashCopy V2 operations, source tracks are copied to the target volume in the track locations specified in the FlashCopy establish request.
As soon as the relationship is established, user programs have access to two logical copies of the source data. Updates to the source volume after the FlashCopy relationship is established are not part of the logical copy on the target device.
Data that is read from the target device returns source track data from the point-in-time of the FlashCopy establish. This is done without waiting for the physical track copy to complete. The FlashCopy relationship ends for each track set when it is copied to the target device. If you update a track on a target device while source tracks are being copied, the data on the target track contains your updated data. The updated track is withdrawn from the FlashCopy relationship. A read operation from the target device for tracks that you updated always returns your updated data.
After the background copy is complete, the data on the target device is the same as the source device when the FlashCopy relationship was first established. Exception: If you modify the target tracks within the track extents, the data on the target device is not the same as the source device.
When the background copy operation completes, the FlashCopy relationship ends and the ESS resources that maintain the relationships are released.Note: Background copy is not allowed with space efficient targets. - NOCOPY suppresses the background copy.
The FlashCopy NOCOPY mode causes the relationship to be established without immediately initiating a background copy. When the ESS receives an update to a source track in a FlashCopy relationship, a copy of the point-in-time (pre-update) data is preserved on the target volume. Data that is read from the target device returns source track data from the point-in-time of the FlashCopy establish.
A FlashCopy relationship established in NOCOPY mode remains active until one of the following occurs:- All specified source device tracks are updated by user applications.
- The ESS copies all tracks from source to target when a threshold number of source tracks are updated.
- A FlashCopy withdraw (using the FCWITHDR command) is issued to remove the FlashCopy relationship.
- A NOCOPY relationship is converted to a COPY relationship through the NOCOPY2COPY function.
Figure 1. How the NOCOPY relationship works
When a FlashCopy NOCOPY relationship is ended, the track data on the target device is unpredictable and should not be used. If updates occur to source device tracks in the FlashCopy NOCOPY relationship, a copy of the source tracks from the point-in-time of the FlashCopy establish might not have been physically written to the target device at the time the withdraw occurs.
Note: When the target of a relationship is space efficient, the FlashCopy mode must be NOCOPY. - NOCOPY2COPY changes the existing FlashCopy relationship from
NOCOPY to COPY.
When one or more NOCOPY relationships exists for a source volume, NOCOPY2COPY initiates a background copy for all target relationships with intersecting source extents from the point in time the NOCOPY was issued. Upon completion of the background copy, the converted relationship(s) are terminated.
There must be an existing FlashCopy relationship between source and target. If one does not exist, none is created.Note: When the target of a relationship is space efficient, do not use NOCOPY2COPY. - ASYNC is only used for establishing FlashCopy relationship between PPRC secondaries and their target volumes in a Global Mirror environment.