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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3566) Custom Replication Policy for Azure
Date Tue, 18 Sep 2012 16:06:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3566?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13457900#comment-13457900

Tsz Wo (Nicholas), SZE commented on HDFS-3566:

Hi Suma, I think your command is correct but test-patch got stuck in building the cn-docs.
 I just have filed HADOOP-8823 for removing the cn-docs dependency.

Below is the test-patch result for your patch.  The findbugs warnings are not related.
     [exec] -1 overall.  
     [exec]     +1 @author.  The patch does not contain any @author tags.
     [exec]     +1 tests included.  The patch appears to include 3 new or modified tests.
     [exec]     +1 javadoc.  The javadoc tool did not generate any warning messages.
     [exec]     +1 javac.  The applied patch does not increase the total number of javac compiler
     [exec]     -1 findbugs.  The patch appears to introduce 11 new Findbugs (version 1.3.9)
> Custom Replication Policy for Azure
> -----------------------------------
>                 Key: HDFS-3566
>                 URL: https://issues.apache.org/jira/browse/HDFS-3566
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Sumadhur Reddy Bolli
>            Assignee: Sumadhur Reddy Bolli
>             Fix For: 1-win
>         Attachments: AzureBlockPlacementPolicy.pdf, azurepolicy-branch-1-win.patch
> Azure has logical concepts like fault and upgrade domains. Each fault domain spans multiple
upgrade domains and each upgrade domain spans multiple fault domains. Machines are spread
typically evenly across both fault and upgrade domains. Fault domain failures are typically
catastrophic/unplanned failures and data loss possibility is high. An upgrade domain can be
taken down by azure for maintenance periodically. Each time an upgrade domain is taken down
a small percentage of machines in the upgrade domain(typically 1-2%) are replaced due to disk
failures, thus losing data. Assuming the default replication factor 3, any 3 data nodes going
down at the same time would mean potential data loss. So, it is important to have a policy
that spreads replicas across both fault and upgrade domains to ensure practically no data
loss. The problem here is two dimensional and the default policy in hadoop is one-dimensional.
This policy would spread the datanodes across atleast 2 fault domains and three upgrade domains
to prevent data loss.

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