Branch b1_6

  Severity   : normal
  Frequency  : when qunit size is too small(less than 20M)
  Bugzilla   : 12588
  Description: write is stopped by improper -EDQUOT
  Details    : If the master is busy and qunit size is small enough(let's say 1M),
  	     the slave can not get quota from master on time, which will lead
  	     slave to trigger a -EQUOTA to client.

  b=12588
  i=green
  i=wangdi