When there are files having a lease but are not under construction, NN will fail to start up with
15/05/12 00:36:31 ERROR namenode.FSImage: Unable to save image for /hadoop/hdfs/namenode
The actually problem is that the image could be corrupted by bugs like
HDFS-7587. We should have an option/conf to allow NN to start up so that the problematic files could possibly be deleted.