Correct, replication will go from the hot bucket on node 1 to the cold bucked on node 2.
If the cold bucket is "optimized for reads", there will be some penalty on write performance causing replication times to be increased. But for cold, spindle count + read caching is optimal for the sequential repl traffic
In reality what you're really focusing on is the rate at which data can be read from that replica in the case that the originating node fails.
As always its about finding the correct balance to fit the IO requirements, but replication IO is essentially a secondary operation.
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