Yonghwan Kim created HDFS-4945:
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Summary: A Distributed and Cooperative NameNode Cluster for a
Highly-Available HDFS
Key: HDFS-4945
URL: https://issues.apache.org/jira/browse/HDFS-4945
Project: Hadoop HDFS
Issue Type: New Feature
Components: auto-failover
Affects Versions: HA branch (HDFS-1623)
Reporter: Yonghwan Kim
Recently, Hadoop attracts much attention of engineers and researchers as an
emerging and effective framework for Big Data.
HDFS(Hadoop Distributed File System) can manage huge amount of data with
guaranteeing high performance and reliability
with only commodity hardware.
However, HDFS requires a single master node, called NameNode, to manage the
entire namespace (or all the i-nodes)
of a file system. This causes SPOF (Single Point Of Failure) problem because
the file system becomes inaccessible
when the NameNode fails. (HDFS-2064)
This also causes a bottleneck of efficiency since all the access requests to
the file system have to contact the
NameNode. Hadoop 2.0 resolves the SPOF problem by introducing manual failover
based on two NameNodes, Active and Standby.
However, it still has the efficiency bottleneck problem since all the access
requests have to contact the Active
in ordinary executions. It may also lose an advantage of using commodity
hardware since the two NameNodes have to
share a highly-reliable sophisticated storage.
We here propose a new HDFS architecture to resolve all the problems mentioned
above.
The proposed architecture has the following features and advantages.
1. Multiple NameNodes (not restricted to two) can be utilized to improve
availability.
The entire namespace of a file system is partitioned into several fragments,
and replicas of each fragment are
dispersed among the NameNodes. When each fragment has k replicas, the file
system can tolerate up to
floor(k/2 - 1) faulty NameNodes.
2. Multiple NameNodes can be utilized to improve performance. The performance
bottleneck caused by a single
NameNode can be circumvented by assigning different NameNodes to different
fragments as the primary ones
(or the entry points).
3. The highly-reliable storage shared by the NameNodes is removed by
introducing message-based consistency
mechanism among the NameNodes. The architecture requires only commodity
hardware.
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