In my scenario:
1. One region server has more than 1,000 regions.(hdf hard disk capacity(12T) / 3 (replication) /
region size = 2G).
2. One moment, Dozens of Regions per region server are working for put operation.
I went through the balance code , I found current balnace algorithm is invalid for our scenarios.
1)When adds one new machine to our cluster, Maybe all of hot regions(is working) will move to this one.
2)When one RS restarts, Maybe all of hot regions(is working) will move to this machine.