Which config parameter can make ES 2.1's default write replica action from sync to async?

Elastic Stack Elasticsearch
1

we don't want to sync write to replica. So we'd like to modified it.

2

You cannot, it is no longer configurable in 2.X.

3

so the only way to asyn is to let client change it, right?

4

No, you cannot do it. At all.

5

under this situation, when a shard is down, how ES deal with write request? will it wait for recovery then execute write or it will response fail to client before recovery?

6

Write consistency still applies here, so it depends on how many replicas you have.