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From "Sumadhur Reddy Bolli (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3566) Custom Replication Policy for Azure
Date Tue, 26 Jun 2012 01:22:42 GMT
Sumadhur Reddy Bolli created HDFS-3566:
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             Summary: 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


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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