as I have said in previous comment：
“eventually consistent stands for all replica will eventually consistent, say master replica down , and it would recopy those updates which has not been sent to replicas.
but couchbase here no mater replicateTo=1 or not, it will loss those updates which has not replicated yet if master replica down even if return back”
replicateTo=1 has a bad case: master write mem or persist success, and replication failed, it return fail, but master and replica is not consistent at this time , and will not eventually consistent.
although it has callback function to let client do sth. but the server itself should follow BASE protocol , and callback to write back the old value would fail as well