>DataNode rejoins take care of only NameNode. Sorry didn't get this
From: Narasingu Ramesh [mailto:ramesh.narasi...@gmail.com] Sent: Tuesday, September 11, 2012 2:38 PM To: user@hadoop.apache.org Subject: Re: what happens when a datanode rejoins? Hi Mehul, DataNode rejoins take care of only NameNode. Thanks & Regards, Ramesh.Narasingu On Tue, Sep 11, 2012 at 2:36 PM, Mehul Choube <mehul_cho...@symantec.com<mailto:mehul_cho...@symantec.com>> wrote: > The namenode will asynchronously replicate the blocks to other datanodes in > order to maintain the replication factor after a datanode has not been in > contact for 10 minutes. What happens when the datanode rejoins after namenode has already re-replicated the blocs it was managing? Will namenode ask the datanode to discard the blocks and start managing new blocks? Or will namenode discard the new blocks which were replicated due to unavailability of this datanode? Thanks, Mehul From: George Datskos [mailto:george.dats...@jp.fujitsu.com<mailto:george.dats...@jp.fujitsu.com>] Sent: Tuesday, September 11, 2012 12:56 PM To: user@hadoop.apache.org<mailto:user@hadoop.apache.org> Subject: Re: what happens when a datanode rejoins? Hi Mehul Some of the blocks it was managing are deleted/modified? The namenode will asynchronously replicate the blocks to other datanodes in order to maintain the replication factor after a datanode has not been in contact for 10 minutes. The size of the blocks are now modified say from 64MB to 128MB? Block size is a per-file setting so new files will be 128MB, but the old ones will remain at 64MB. What if the block replication factor was one (yea not in most deployments but say incase) so does the namenode recreate a file once the datanode rejoins? (assuming you didn't perform a decommission) Blocks that lived only on that datanode will be declared "missing" and the files associated with those blocks will be not be able to be fully read, until the datanode rejoins. George
