Use Redirect-on-Write for DRP Fully Allocated volumes

For FlashCopy (FC) to use Redirect-on-Write (RoW) instead of Copy-on-Write (CoW) in a Data Reduction Pool (DRP), current implementation requires both the source and the target volumes to be compressed + deduplicated, as the dedup reference counting mechanism is used to avoid copying the data.
Utilization of some Fully-allocated volumes in DRP is often necessary, to provide the performance benefits of not adding the DRP write amplification from directory reads/updates. But this currently eliminates the benefits of RoW for FC. This is particularly problematical for multiple-target FC, most specifically for a source volume that uses FC for both Change Volume mappings for GMCV replication, and for Point-in-Time FlashCopy (PiT FC) mappings, such as SafeGuarded Copy. In this scenario, CoW requires ‘Cleaning’ of the Change Volume to the newest PiT FC volume every single GMCV cycle period.
This RFE is to request that FC RoW be supported for cases where the source volume in a DRP is Fully Allocated, but the FC target volumes are Compressed + Deduplicated. Realizing that CoW might be necessary for the newest FC in the chain, since the fully-allocated source volume does not have LSA/DRP directory entries on which RoW can act. But if multi-target FC target volumes are all configured as Compressed + Deduplicated volumes, the performance impact of ‘Cleaning’ due to FlashCopy dependencies could be eliminated (actually, drastically reduced, with only directory reads/updates required instead of potentially mulitple GB of data copy) if the multiple FC dependencies utilize a RoW mechanism.