Elasticsearch moving all shards once a node getting full

[suanmeiguo (Vincent)]

I have the config cluster.routing.allocation.disk.watermark.high:85% and I notice that once a node cross 85% threshold, Elasticsearch starts relocating all shards out from that node.

It is strange to me because it'll drop below 85% if it just move one of them. Is there a config I can control on this? or is this a expected behavior for elasticsearch?

I'm using Elasticsearch 2.4.1

Thank you

[suanmeiguo (Vincent)]

Here's a screenshot of the disk usage for the cluster. You can see Friday around 2AM the cluster starts to struggle on disk. And new lines are added to the graph those are new nodes I added to comfort the cluster.