456 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
Table 11-4 lists the indirection layer algorithm in a multi-target FlashCopy.
Table 11-4   Summary table of the FlashCopy indirection layer algorithm t
Stopping process in a Multiple Target FlashCopy - Cleaning Mode
When a mapping that contains a target that has dependent mappings is stopped, the 
mapping enters the stopping state. It then begins copying all grains that are uniquely held on 
the target volume of the mapping that is being stopped to the next oldest mapping that is in 
the copying state. The mapping remains in the stopping state until all grains are copied, and 
then enters the stopped state. This mode is referred to as the Cleaning Mode. 
For example, if the mapping Source-T2 was stopped, the mapping enters the stopping state 
while the cleaning process copies the data of T2 to T1 (next oldest). After all of the data is 
copied, Source-T2 mapping enters the stopped state, and T1 is no longer dependent upon 
T2. However, T0 remains dependent upon T1.
For example, with Table 11-3 on page 454, if you stop the Source-T2 mapping on “Time 7,” 
the grains that are not yet copied on T1 are copied from T2 to T1. Reading T1 is then like 
reading the source at the time T1 was started (“Time 2”).
As another example, with Table 11-3 on page 454, if you stop the Source-T1 mapping on 
“Time 8,” the grains that are not yet copied on T0 are copied from T1 to T0. Reading T0 is 
then like reading the source at the time T0 was started (“Time 0”).
If you stop the Source-T1 mapping while Source-T0 mapping and Source-T2 are still in 
copying mode, the grains that are not yet copied on T0 are copied from T1 to T0 (next oldest). 
T0 now depends upon T2.
Your target volume is still accessible while the cleaning process is running. When the system 
is operating in this mode, it is possible that host I/O operations can prevent the cleaning 
process from reaching 100% if the I/O operations continue to copy new data to the target 
volumes.
Accessed 
Volume
Was the grain 
copied?
Host I/O operation
Read Write
Source No Read from the source 
volume.
Copy grain to most recently 
started target for this source, 
then write to the source.
Yes Read from the source 
volume.
Write to the source volume.
Target No If any newer targets exist for 
this source in which this grain 
was copied, read from the 
oldest of these targets. 
Otherwise, read from the 
source.
Hold the write. Check the 
dependency target volumes 
to see whether the grain was 
copied. If the grain is not 
copied to the next oldest 
target for this source, copy 
the grain to the next oldest 
target. Then, write to the 
target.
Yes Read from the target volume. Write to the target volume.