增加Arbiter
增加配置文件mongod1,mongod2,mongod3分别为shard1，shard2，shard3三个set集合的arbiter。
replSet=shard1 replSet=shard2 replSet=shard3
启动mongod实例。
连接Primary.
rs.addArb(“192.168.1.50:10001″) rs.addArb(“192.168.1.50:10002″) rs.addArb(“192.168.1.50:10003″)
移除Arbiter
rs.remove(“192.168.1.50:10001″)
注意:最好移除结点时候先停掉服务，防止有特殊未知状态出现。
Note:Before running the rs.remove() operation, you must shut down the replica set member that you're removing.
Changed in version 2.2: This procedure is no longer required when using rs.remove(), but it remains good practice.