Chapter 11. Advanced Copy Services 455
An intermediate target disk (not the oldest or the newest) treats the set of newer target 
volumes and the true source volume as a type of composite source. It treats all older volumes 
as a kind of target (and behaves like a source to them).
Target read with Multiple Target FlashCopy
Target reading with multiple targets depends on whether the grain was copied:
/SM590000If the grain that is being read is copied from the source to the target, the read returns data 
from the target that is being read.
/SM590000If the grain is not yet copied, each of the newer mappings is examined in turn. The read is 
performed from the first copy (the oldest) that is found. If none is found, the read is 
performed from the source. 
For example, as shown in Figure 11-13 on page 454, if the yellow grain on T2 is read, it 
returns “H” because there is no newer target than T2. Therefore, the source is read.
As another example, as shown in Figure 11-13 on page 454, if the red grain on T0 is read, 
it returns “E” because there are two newer targets for T0, and T1 is the oldest of them.
Target write with Multiple Target FlashCopy (Copy on Demand)
A write to an intermediate or the newest target volume must consider the state of the grain 
within its own mapping, and the state of the grain of the next oldest mapping. Consider the 
following points:
/SM590000If the grain in the target that is being written is copied and if the grain of the next oldest 
mapping is not yet copied, the grain must be copied before the write can proceed to 
preserve the contents of the next oldest mapping. 
For example, as shown in Figure 11-13 on page 454, if the grain “G” is changed on T2, 
then it needs to be copied to T1 (next oldest not yet copied) first and then changed on T2.
/SM590000If the grain in the target that is being written is not yet copied, the grain is copied from the 
oldest copied grain in the mappings that are newer than the target, or from the source if 
none is copied. For example, as shown in Figure 11-13 on page 454, if the red grain on T0 
is written, then it will first be copied from T1 (data “E”). After this copy is done, the write 
can be applied to the target.
Time 3: change of “E” is 
made on source (->“H”)
G B C
D H F
A _ _
_ _ _
_ _ _*
_ E_
Not started
Time 4: mapping with T2 
is started
G B C
D H F
A _ _
_ _ _
_ _ _
_ E_
_ _ _*
_ _ _
Time 5: change of “F” is 
made on source (->“I”)
G B C
D H I
A _ _
_ _ _
_ _ _
_ E_
_ _ _*
_ _ F
Time 6: change of “G” is 
made on source (->“J”)
J B C
D H I
A _ _
_ _ _
_ _ _
_ E_
G _ _*
_ _ F
Time 7: stop of 
Source-T2 mapping
J B C
D H I
A _ _
_ _ _
G _ _ *
_ E F
Stopped
Time 8: stop of 
Source-T1 mapping
J B C
D H I
A _ _ *
_ E F
Stopped Stopped
* “most recent” target
Source Volume Target T0 Target T1 Target T2