Yes, checkpoints are helpful when your original NN image goes corrupt (very very rare, if you use dual or more dfs.name.dir points to be safe).
On 27-Dec-2011, at 12:33 PM, praveenesh kumar wrote: > Cool. > I just did that.. > So now I am seeing my fsimage file on SNN's hadoop.tmp.dir... > So incase my NN went down.. I can take this image file from SNN and paste > it at NN's *dfs.name.dir/current/fsimage * > and I can have NN up based on last snapshot that SNN had, right ? > > Thanks, > Praveenesh > > On Tue, Dec 27, 2011 at 12:20 PM, Harsh J <ha...@cloudera.com> wrote: >> The link Uma passed already covered that question: > http://www.cloudera.com/blog/2009/02/multi-host-secondarynamenode-configuration/[dfs.http.address > in hdfs-site.xml pointing to NN_HOST:50070 should d.] >> >> Also, if you are using the tarball start/stop scripts, putting in the > hostname for SNN in the conf/masters list is sufficient to get it > auto-started there. >> >> On 27-Dec-2011, at 11:36 AM, praveenesh kumar wrote: >> >>> Thanks..But, my 1st question is still unanswered. >>> I have a 8 DN/TT machines and 1 NN machine. >>> I want to set one of my DN/TT machine as SNN. >>> How I have to configure my conf/*.xml files to achieve this ? >>> >>> Thanks, >>> Praveenesh >>> >>> On Mon, Dec 26, 2011 at 8:44 PM, Harsh J <ha...@cloudera.com> wrote: >>>> (Answering beyond Uma's reply) >>>> >>>>> Can a DN also act as SNN, any pros and cons of having this > configuration ? >>>> >>>> You can run SNN on a regular slave box if you can't have a dedicate a > box, it shouldn't be an issue for small clusters -- Do ensure its disk > configuration is proper, and its allocated near to the same heap as the > NameNode is. >>>> >>>> For large clusters where the fsimage and periodic edits file sizes are > larger, it would be worth placing it on a separate box given SNN's > interactions. >>>> >>>> On 26-Dec-2011, at 7:53 PM, Uma Maheswara Rao G wrote: >>>> >>>>> Hey Praveenesh, >>>>> >>>>> You can start secondary namenode also by just giving the option > ./hadoop secondarynamenode >>>>> >>>>> DN can not act as seconday namenode. The basic work for seconday > namenode is to do checkpointing and getting the edits insync with Namenode > till last checkpointing period. DN is to store the real data blocks > physically. >>>>> you need to configure correct namenode http address also for the > secondaryNN, so that it can connect NN for checkpointing operations. >>>>> > http://hadoop.apache.org/common/docs/current/hdfs_user_guide.html#Secondary+NameNode >>>>> You can configure secondary node IP in masters file, start-dfs.sh > itself will start the SNN automatically as it starts DN and NN as well. >>>>> >>>>> also you can see > http://www.cloudera.com/blog/2009/02/multi-host-secondarynamenode-configuration/ >>>>> >>>>> Regards, >>>>> Uma >>>>> ________________________________________ >>>>> From: praveenesh kumar [praveen...@gmail.com] >>>>> Sent: Monday, December 26, 2011 5:05 PM >>>>> To: common-user@hadoop.apache.org >>>>> Subject: Secondary Namenode on hadoop 0.20.205 ? >>>>> >>>>> Hey people, >>>>> >>>>> How can we setup another machine in the cluster as Secondary Namenode >>>>> in hadoop 0.20.205 ? >>>>> Can a DN also act as SNN, any pros and cons of having this > configuration ? >>>>> >>>>> Thanks, >>>>> Praveenesh >>>> >>
