Gluster users - Apr 2014 - gluster volume rebalance-brick

Concerning gluster v3.4.2

What does the "rebalance-brick" option do. Details please. There is 
no documentation on this command beyond a terse description in the
man page:

        volume rebalance-brick <VOLNAME>(<BRICK> <NEW-BRICK>)
start
              Start rebalancing the specified volume.

How is this different than ?gluster volume rebalance ??, which is 
documented in detail?

I?m hoping (!) that it performs a rebalance, but limits the migration
to a single brick or pair of bricks. 

Andrew Smith
smith.andrew.james at gmail.com