Chapter 11. Advanced Copy Services 449
11.1.9  Incremental FlashCopy
When a FlashCopy mapping is stopped, either because the entire source volume was copied 
onto the target volume or because a user manually stopped it, the bitmap table is reset. 
Therefore, when the same FlashCopy is started again, the copy process is restarted from the 
beginning.
Using the -incremental option when creating the FlashCopy mapping allows the system to 
keep the bitmap as it is when the mapping is stopped. Therefore, when the mapping is started 
again (at another point-in-time), the bitmap is reused and only changes between the two 
copies are applied to the target.
A system that provides Incremental FlashCopy capability allows the system administrator to 
refresh a target volume without having to wait for a full copy of the source volume to be 
complete. At the point of refreshing the target volume, for a particular grain, if the data 
changed on the source or target volumes, the grain from the source volume is copied to the 
target. 
The advantages of Incremental FlashCopy are only useful if a previous full copy of the source 
volume was obtained. Incremental FlashCopy only helps with further recovery time objectives 
(RTOs, time needed to recover data from a previous state), it does not help with the initial 
RTO.
For example, as shown in Figure 11-11 on page 450, a FlashCopy mapping was defined 
between a source volume and a target volume with the -incremental option. Consider the 
following points:
/SM590000The mapping is started on Copy1 date. A full copy of the source volume is made, and the 
bitmap is updated every time that a grain is copied. At the end of Copy1, all grains were 
copied and the target volume is a replica of the source volume at the beginning of Copy1. 
Although the mapping is stopped (thanks to the -incremental option), the bitmap is 
maintained.
/SM590000Changes are made on the source volume and the bitmap is updated, although the 
FlashCopy mapping is not active. For example, grains E and C on the source are changed 
in G and H, their corresponding bits are changed in the bitmap. The target volume is 
untouched.
/SM590000The mapping is started again on Copy2 date. The bitmap indicates that only grains E and 
C were changed, so only G and H are copied on the target volume. There is no need to 
copy the other grains, as they were already copied the first time. The copy time is much 
quicker than for the first copy as only a fraction of the source volume is copied.