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I wonder if someone with HDFS expertise can chime in here. In general, I have not run into any problem with replication factor being 3 but number of DNs being less than that (yes, some tests such as decommissioning require explicit changing of the value). As you add more DNs HDFS starts adding replicas. The opposite seems to be risky to me. Start with a replication factor of 1 and then add DNs. If you forget to change the value, replicas will not be created. Data that is already stored will not be replicated. So in essence, if one is deploying a cluster that needs to live long "3" is a better value. If the cluster never needs more than 1-2 DN then its likely a test cluster and thus not a higher priority scenario. So I would rather leave the replication factor to be 3 and then have test deployments change defaults based on what they are testing. -1 for the change (the code change is good, but I am not convinced that 1 is a good default) - Sumit Mohanty On Dec. 30, 2015, 11:04 a.m., Matt wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/41795/ > ----------------------------------------------------------- > > (Updated Dec. 30, 2015, 11:04 a.m.) > > > Review request for Ambari, Alexander Denissov, Alejandro Fernandez, bhuvnesh > chaudhary, Dmitro Lisnichenko, jun aoki, Lav Jain, Newton Alex, Oleksandr > Diachenko, Sumit Mohanty, and Srimanth Gunturi. > > > Bugs: AMBARI-14459 > https://issues.apache.org/jira/browse/AMBARI-14459 > > > Repository: ambari > > > Description > ------- > > By default dfs.replication is set to 3. In a single node cluster, advise and > validate dfs.replication = 1 > > > Diffs > ----- > > ambari-server/src/main/resources/stacks/HDP/2.0.6/services/stack_advisor.py > 7e2871b > ambari-server/src/test/python/stacks/2.0.6/common/test_stack_advisor.py > 6699e94 > > Diff: https://reviews.apache.org/r/41795/diff/ > > > Testing > ------- > > Manually Tested > Unit test updated. > > > Thanks, > > Matt > >
