Minor Description
When a bock file is deleted on disk or copied back to the disk, the DirectoryScanner can find the change, but the namenode know the change only untill the next full report. And in big cluster the period of full report is set to long time invterval.
Call notifyNamenodeDeletedBlock if block files are deleted and call notifyNamenodeReceivedBlock if the block files is found agian. So the Incremental block report can send the change to namenode in next heartbeat.