> On Dec. 30, 2015, 9:39 a.m., Sumit Mohanty wrote: > > 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)
I agree with you Sumit! I did not think this through when I started working on this. I'd rather leave the replication factor to be 3 as default, regardless of having or not having less than three DNs. As a user I might start with 1 DN when I start a cluster managed by Ambari, and add 3 DNs the next day. And totally forget that Ambari set the dfs.replication on my cluster to 1 on day 1, and never changed it. As a user, I myself would not want to have the default set to 1 or 2 (based on no of DNs). And leave the default as 3. I can discard the changes and close the JIRA, with no action to be taken, if you agree to it. - Matt ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/41795/#review112324 ----------------------------------------------------------- On Dec. 30, 2015, 3:04 a.m., Matt wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/41795/ > ----------------------------------------------------------- > > (Updated Dec. 30, 2015, 3:04 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 > >
