Quorum, consistency and datacenter awareness?

[HubertChang]

El  ElasticSearch works in the cluster.
Is there a quorum concept? If the replication factor is 2 or 3 and one replication fails, is the content still available?
Is there a param to read from _all_replications and read from _one_replication to maintain the consitency?
Will the replication be datacenter awared in the future?
do these features depends on the gateway? Like Cassandra, all these features is ready.
Thanks.