The following has bearing on understanding what happens to the data store 
when Replicas are increased or decreased.
 
Reading about re-sizing the cluster, I've read
 
- Changing the number of shards requires re-indexing, so it's highly 
recommended to allocate a number of shards consistent with the max number 
of expected nodes in the cluster from the beginning.
 
- Replicas can be added or removed at any time without an unusual load.
 
So, it begs the question, I would expect that adding replicas creates new 
copies.
But, what happens if the number of replicas is decreased? 
Is there a difference changing replica number by runtime command compared 
to starting up a node (elasticsearch.yml), particularly if replica numbers 
are decreased?
I assume that the replica number with the highest number is removed first?
And what about the data, is it automatically purged or left "orphaned" in 
data storage?
 
And if orphaned in data storage, is there a recommended way to manually 
remove the replica data no longer used?
I would also expect that after decreasing the number of replicas, if the 
number is increased again that whole new replicas would be created and 
allocated, none of the old replicas might be checked for integrity and 
possibly re-used (same procedure as recovery).
 
Thx,
Tony

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