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From aajis...@apache.org
Subject hadoop git commit: HDFS-8914. Document HA support in the HDFS HdfsDesign.md. Contributed by Lars Francke.
Date Mon, 21 Dec 2015 12:48:30 GMT
Repository: hadoop
Updated Branches:
  refs/heads/branch-2.7 5ffad1551 -> e0e5a0fa8

HDFS-8914. Document HA support in the HDFS HdfsDesign.md. Contributed by Lars Francke.

(cherry picked from commit 049ccf71ce4457296974f12f5159540f8fcf1ede)

Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/e0e5a0fa
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/e0e5a0fa
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/e0e5a0fa

Branch: refs/heads/branch-2.7
Commit: e0e5a0fa828a975db0b6d1b02fb460d412edc2bb
Parents: 5ffad15
Author: Haohui Mai <wheat9@apache.org>
Authored: Sun Nov 22 16:10:27 2015 -0800
Committer: Akira Ajisaka <aajisaka@apache.org>
Committed: Mon Dec 21 21:44:46 2015 +0900

 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt                     | 3 +++
 hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 2dad550b..92e0ef0 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -42,6 +42,9 @@ Release 2.7.3 - UNRELEASED
     HDFS-9505. HDFS Architecture documentation needs to be refreshed.
     (Masatake Iwasaki via aajisaka)
+    HDFS-8914. Document HA support in the HDFS HdfsDesign.md.
+    (Lars Francke via wheat9)
 Release 2.7.2 - UNRELEASED

diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md b/hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md
index 786db42..482b007 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md
@@ -193,7 +193,7 @@ It is possible that a block of data fetched from a DataNode arrives corrupted.
 The FsImage and the EditLog are central data structures of HDFS. A corruption of these files
can cause the HDFS instance to be non-functional. For this reason, the NameNode can be configured
to support maintaining multiple copies of the FsImage and EditLog. Any update to either the
FsImage or EditLog causes each of the FsImages and EditLogs to get updated synchronously.
This synchronous updating of multiple copies of the FsImage and EditLog may degrade the rate
of namespace transactions per second that a NameNode can support. However, this degradation
is acceptable because even though HDFS applications are very data intensive in nature, they
are not metadata intensive. When a NameNode restarts, it selects the latest consistent FsImage
and EditLog to use.
-The NameNode machine is a single point of failure for an HDFS cluster. If the NameNode machine
fails, manual intervention is necessary. Currently, automatic restart and failover of the
NameNode software to another machine is not supported.
+Another option to increase resilience against failures is to enable High Availability using
multiple NameNodes either with a [shared storage on NFS](./HDFSHighAvailabilityWithNFS.html)
or using a [distributed edit log](./HDFSHighAvailabilityWithQJM.html) (called Journal). The
latter is the recommended approach.
 ### Snapshots

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