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>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] > *Sent:* Tuesday, September 11, 2012 12:56 PM > *To:* 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**** >