We support human readable units now. The default balancing bandwidth in the conf is "10m". However, human readable units are not supported by dfsadmin -setBalancerBandwidth. This means you can't pass the output of "hdfs getconf -confKey dfs.datanode.balance.bandwidthPerSec" to "hdfs dfsadmin -setBalancerBandwidth".
This is a regression from pre-human readable units.