See comments in HBASE-7247: the master checks the time spent by the regionserver, and assign it to another if it takes too long. It adds complexity.
from Stack: "I'm currently of the opinion that this expensive facility of master failing an open because it has been taking too long on a particular regionserver has been of no use – worse, it has only caused headache – but I may be just not remembering and others out on dev list will have better recall than I." So, opinions & memories are more than welcome. Removing this feature would be a huge simplification! Cheers, Nicolas
