I have a cluster using HBase 1.1.2 where I have a table and a local index (using Apache Phoenix 4.6) in total both tables have 300 regions (aprox: 18 regions per server), my hbase.hregion.max.filesize=30GB and my region sizes are now ~4.5GB compressed (~7GB uncompressed). However each time I restart a RS sometimes a region gets split. This is unexpected because my key space is uniform (using MD5) and if the problem was my region.size >  hbase.hregion.max.filesize I would expect to have all the regions or almost all splitting but this only happens when I restart a RS and it happens only for 1 or 2 regions.

What are the different scenarios where a region can split?

What are the right steps to restart a region server in order to avoid these unexpected splits?

Thank you,