450 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
Figure 11-11   Incremental FlashCopy example
11.1.10  Starting FlashCopy mappings and Consistency Groups
You can perform the actions of preparing, starting, or stopping FlashCopy on a stand-alone 
mapping or a Consistency Group.
When using the CLI to perform FlashCopy on volumes, before you start a FlashCopy 
(regardless of the type and options specified), issue a prestartfcmap or 
prestartfcconsistgrp command. These commands put the cache into write-through mode 
and provides a flushing of the I/O that is bound for your volume. After FlashCopy is started, an 
effective copy of a source volume to a target volume is created.
The content of the source volume is presented immediately on the target volume and the 
original content of the target volume is lost.
FlashCopy commands can then be issued to the FlashCopy Consistency Group and 
therefore, simultaneously for all of the FlashCopy mappings that are defined in the 
Consistency Group. For example, when a FlashCopy start command is issued to the 
Consistency Group, all of the FlashCopy mappings in the Consistency Group are started at 
the same time. This simultaneous start results in a point-in-time copy that is consistent across 
all of the FlashCopy mappings that are contained in the Consistency Group.
Rather than using prestartfcmap or prestartfcconsistgrp, you can also use the -prep 
parameter in the startfcmap or startfcconsistgrp command to prepare and start 
FlashCopy in one step.