HDFS-12911 modularization is introducing BlockMoveTaskHandler interface for moving the file blocks. That will help us to plugin different ways of block move mechanisms, if needed.
For Internal SPS, we have simple blk movement tasks to target DN descriptors. For external SPS, we should have mechanism to send replaceBlock on target node and have a listener to track the block movement completion.
This is the task to implement the ExternalSPSBlockMoveTaskHandler plugin for external SPS.