how does one rebalance data nodes

[prasana.iyengar]

1. After adding new data nodes is there a way to force a rebalance the data blocks across the new nodes.
We recently added 6 nodes to the cluster - the original 4 nodes seem to have 80+% hdfs usage.
2. In 0.16.0 i also have the following settings in hadoop-site.xml - .
 dfs.datanode.du.reserved - 10G [default = 0]
 dfs.datanode.du.pct - 0.9f [default = 0.98f]

Q:will this stop the fillup of the data node @ 90% and/or 10G remaining on the partition [whichever is earlier] ?

thanks,
-prasana