config = {"_id" : "gpower" , "members" : [{"_id" : 0 , "host" : "192.168.2.4:27017"},{"_id" : 1 , "host" : "192.168.2.6:27017", "priority" : "0", "votes":"0"}]}
副本集初始化配置时，可以将备份节点的优先级和选举都设为0 : "priority" : "0", "votes":"0"
如果想要将备份节点变为主节点 :
var config = rs.config()
config.member[1].priority = 1
config.member[1].votes = 1
config.member[0].priority = 0
config.member[0].votes = 0
rs.reconfig(config, {"face" : true})
