Why not remove the block on the disk if the snapshot?

hadoop version 2.4.1. I have tested the snapshot. 1. upload file, /tmp/test.avi 2. create snapshot, /tmp snap1 3. delete file, /tmp/test.avi 4. moved to the Trash, /user/hadoop/.Trash/tmp/test.avi 5. file deleted in trash. 6. but, blocks is not deleted in datanode disk. why?? 7. delete snap

mismatch layout version.

I installed version 2.4.1. I found the following information in the datanode log file. But, cluster is healthy. *** datanode log 2014-07-21 15:43:27,365 INFO org.apache.hadoop.hdfs.server.common.Storage: Data-node version: -55 and name-node layout version: -56

Why does suddenly ha switching?

hadoop version 2.4.1 Network is in good condition. What causes the session timeout? ** DFSZKFailoverController logs2014-08-11 17:20:13,226 DEBUG org.apache.zookeeper.ClientCnxn: Got ping response for sessionid: 0x147a0162d86000c after 0ms2014-08-11 17:20:27,012 INFO org.apache.zookeeper