FSNamesystem.delete() maybe cause data residue when active namenode crash or shutdown

Consider the following scenario：

(1) User delete a hdfs dir with many blocks.

(2) Then ative Namenode is crash or shutdown or failover to standby Namenode  by administrator

(3) This may result in residual data

FSNamesystem.delete() will

(1)delete dir first

(2)add toRemovedBlocks into markedDeleteQueue. 

(3) MarkedDeleteBlockScrubber Thread will consumer the markedDeleteQueue and delete blocks.

If the active namenode crash, the blocks in markedDeleteQueue will be lost and never be deleted. And the block cloud not find via hdfs fsck command. But it is alive in datanode disk.

Thus , 

SummaryA =  hdfs dfs -du -s / 

SummaryB =sum( datanode report dfsused)

SummaryA < SummaryB

This may be unavoidable.  But is there any way to find out the blocks that should be deleted and clean it ?