Thanks for your answer!
There also some viewpoints show that we should keep shards number per node small.
Like this answer : https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!topic/elasticsearch/hrq_z2qtNmo
and this experiment : http://blog.trifork.com/2014/01/07/elasticsearch-how-many-shards/
How can I keep balance between “light and easy to reallocation” and “more shard use more resource”？