Hi, 1) You may want to read about proper node decommissioning. http://wiki.apache.org/hadoop/FAQ#I_want_to_make_a_large_cluster_smaller_by_taking_out_a_bunch_of_nodes_simultaneously._How_can_this_be_done.3F
2) NameNode will replicate blocks when they do not comply with their replication factor. 3) NameNode does not give up. 4) Yes, ultimately, if you have a replication factor of n and the n replicas are lost at the same time, well, the data is truly lost. But that's not specific to Hadoop. Bertrand On Sun, Oct 27, 2013 at 7:42 PM, Koert Kuipers <[email protected]> wrote: > i have a cluster with replication factor 2. wit the following events in > this order, do i have data loss? > > 1) shut down a datanode for maintenance unrelated to hdfs. so now some > blocks only have replication factor 1 > > 2) a disk dies in another datanode. let's assume some blocks now have > replication factor 0 since they were on this disk that died and on the > datanode that is shut down for maintenance. > > 3) bring back up the datanode that was down for maintenance. > > what i am worried about is that the namenode gives up on a block with > replication factor 0 after steps 1) and 2) and considers it lost, and by > the time the replica will come back on again in step 3) the namenode no > longer considers the block to be existent. > > thanks! koert > > -- Bertrand Dechoux
