Chapter 11. Advanced Copy Services 445
Performing a write operation on the target generates one of the following actions, depending 
on the bitmap:
/SM590000If the bitmap indicates the grain to be modified on the target is not yet copied, it is first 
copied from the source (copy on demand). The bitmap is updated, and the grain is 
modified on the target with the new value, as shown in Figure 11-7. The source volume 
remains unchanged.
Figure 11-7   Modifying a non-copied grain on the target
/SM590000If the bitmap indicates the grain to be modified on the target was copied, it is directly 
changed. The bitmap is not updated, and the grain is modified on the target with the new 
value, as shown in Figure 11-8.
Figure 11-8   Modifying an already copied grain on the Target
Note: If the entire grain is to be modified and not only part of it (some blocks only), the 
copy on demand is bypassed. The bitmap is updated, and the grain on the target is 
modified but not copied first.