Chapter 10. Copy services 499
In Figure 10-7 on page 498, Target 0 is not dependent on a source because it completed
copying. Target 0 has two dependent mappings (Target 1 and Target 2).
Target 1 depends on Target 0. It remains dependent until all of Target 1 is copied. Target 2
depends on it because Target 2 is 20% copy complete. After all of Target 1 is copied, it can
then move to the idle_copied state.
Target 2 is dependent upon Target 0 and Target 1 and remains dependent until all of Target 2
is copied. No target depends on Target 2; therefore, when all of the data is copied to Target 2,
it can move to the idle_copied state.
Target 3 completed copying, so it is not dependent on any other maps.
Target writes with Multiple Target FlashCopy
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.
If the grain of the next oldest mapping is not yet copied, it must be copied before the write can
proceed, to preserve the contents of the next oldest mapping. The data that is written to the
next oldest mapping comes from a target or source.
If 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. After this copy is done, the write can be applied to the target.
Target reads with Multiple Target FlashCopy
If the grain being read is copied from the source to the target, the read returns data from the
target that is being read. If the grain is not yet copied, each of the newer mappings is
examined in turn, and the read is performed from the first copy that is found. If none is found,
the read is performed from the source.
Stopping the copy process
When a stop command is issued to a mapping that contains a target that has dependent
mappings, the mapping enters the stopping state and 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.
For example, if the mapping that is associated with Target 0 was issued a stopfcmap or
stopfcconsistgrp command, Target 0 enters the stopping state while a process copies the
data of Target 0 to Target 1. After all of the data is copied, Target 0 enters the stopped state,
and Target 1 is no longer dependent upon Target 0; however, Target 1 remains dependent on
Target 2.
Note: The stopping copy process can be ongoing for several mappings that share the
source at the same time. At the completion of this process, the mapping automatically
makes an asynchronous state transition to the stopped state, or the idle_copied state if
the mapping was in the copying state with progress = 100%.
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