Repository: hadoop
Updated Branches:
refs/heads/branch-2.6 a4b54dfc8 -> b2a7bbf4f
HDFS-7230. Add rolling downgrade documentation. Contributed by Tsz Wo Nicholas
Sze.
Conflicts:
hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/b2a7bbf4
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/b2a7bbf4
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/b2a7bbf4
Branch: refs/heads/branch-2.6
Commit: b2a7bbf4f6d30dd24f132a634226b38385c2963b
Parents: a4b54df
Author: Jing Zhao <[email protected]>
Authored: Thu Oct 30 10:47:05 2014 -0700
Committer: Jing Zhao <[email protected]>
Committed: Thu Oct 30 10:49:30 2014 -0700
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hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt | 2 +
.../src/site/xdoc/HdfsRollingUpgrade.xml | 77 +++++++++++++++++---
2 files changed, 67 insertions(+), 12 deletions(-)
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http://git-wip-us.apache.org/repos/asf/hadoop/blob/b2a7bbf4/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
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diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 268f9de..bb38230 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -292,6 +292,8 @@ Release 2.6.0 - UNRELEASED
HDFS-6988. Improve HDFS-6581 eviction configuration (Xiaoyu Yao via Colin
P. McCabe)
+ HDFS-7230. Add rolling downgrade documentation. (szetszwo via jing9)
+
OPTIMIZATIONS
HDFS-6690. Deduplicate xattr names in memory. (wang)
http://git-wip-us.apache.org/repos/asf/hadoop/blob/b2a7bbf4/hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsRollingUpgrade.xml
----------------------------------------------------------------------
diff --git
a/hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsRollingUpgrade.xml
b/hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsRollingUpgrade.xml
index 61d7d06..1053695 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsRollingUpgrade.xml
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsRollingUpgrade.xml
@@ -152,17 +152,21 @@
or, in some unlikely case, the upgrade fails (due to bugs in the newer
release),
administrators may choose to downgrade HDFS back to the pre-upgrade
release,
or rollback HDFS to the pre-upgrade release and the pre-upgrade state.
- Both downgrade and rollback require cluster downtime and are not done in a
rolling fashion.
</p>
<p>
- Note that downgrade and rollback are possible only after a rolling upgrade
is started and
+ Note that downgrade can be done in a rolling fashion but rollback cannot.
+ Rollback requires cluster downtime.
+ </p>
+ <p>
+ Note also that downgrade and rollback are possible only after a rolling
upgrade is started and
before the upgrade is terminated.
An upgrade can be terminated by either finalize, downgrade or rollback.
Therefore, it may not be possible to perform rollback after finalize or
downgrade,
or to perform downgrade after finalize.
</p>
+ </section>
- <subsection name="Downgrade" id="Downgrade">
+ <section name="Downgrade" id="Downgrade">
<p>
<em>Downgrade</em> restores the software back to the pre-upgrade release
and preserves the user data.
@@ -174,21 +178,70 @@
A newer release is downgradable to the pre-upgrade release
only if both the namenode layout version and the datenode layout version
are not changed between these two releases.
- Below are the steps for downgrade:
</p>
- <ul>
- <li>Downgrade HDFS<ol>
+
+ <subsection name="Downgrade without Downtime" id="DowngradeWithoutDowntime">
+ <p>
+ In a HA cluster,
+ when a rolling upgrade from an old software release to a new software
release is in progress,
+ it is possible to downgrade, in a rolling fashion, the upgraded machines
back to the old software release.
+ Same as before, suppose <em>NN1</em> and <em>NN2</em> are respectively in
active and standby states.
+ Below are the steps for rolling downgrade:
+ </p>
+ <ol>
+ <li>Downgrade <em>DNs</em><ol>
+ <li>Choose a small subset of datanodes (e.g. all datanodes under a
particular rack).</li>
+ <ol>
+ <li>Run "<code><a href="#dfsadmin_-shutdownDatanode">hdfs dfsadmin
-shutdownDatanode <DATANODE_HOST:IPC_PORT> upgrade</a></code>"
+ to shutdown one of the chosen datanodes.</li>
+ <li>Run "<code><a href="#dfsadmin_-getDatanodeInfo">hdfs dfsadmin
-getDatanodeInfo <DATANODE_HOST:IPC_PORT></a></code>"
+ to check and wait for the datanode to shutdown.</li>
+ <li>Downgrade and restart the datanode.</li>
+ <li>Perform the above steps for all the chosen datanodes in the subset
in parallel.</li>
+ </ol>
+ <li>Repeat the above steps until all upgraded datanodes in the cluster
are downgraded.</li>
+ </ol></li>
+ <li>Downgrade Active and Standby <em>NNs</em><ol>
+ <li>Shutdown and downgrade <em>NN2</em>.</li>
+ <li>Start <em>NN2</em> as standby normally. (Note that it is incorrect
to use the
+ "<a href="#namenode_-rollingUpgrade"><code>-rollingUpgrade
downgrade</code></a>"
+ option here.)
+ </li>
+ <li>Failover from <em>NN1</em> to <em>NN2</em>
+ so that <em>NN2</em> becomes active and <em>NN1</em> becomes
standby.</li>
+ <li>Shutdown and upgrade <em>NN1</em>.</li>
+ <li>Start <em>NN1</em> as standby normally. (Note that it is incorrect
to use the
+ "<a href="#namenode_-rollingUpgrade"><code>-rollingUpgrade
downgrade</code></a>"
+ option here.)
+ </li>
+ </ol></li>
+ <li>Finalize Rolling Downgrade<ul>
+ <li>Run "<code><a href="#dfsadmin_-rollingUpgrade">hdfs dfsadmin
-rollingUpgrade finalize</a></code>"
+ to finalize the rolling downgrade.</li>
+ </ul></li>
+ </ol>
+ <p>
+ Note that the datanodes must be downgraded before downgrading the namenodes
+ since protocols may be changed in a backward compatible manner but not
forward compatible,
+ i.e. old datanodes can talk to the new namenodes but not vice versa.
+ </p>
+ </subsection>
+ <subsection name="Downgrade with Downtime" id="DowngradeWithDowntime">
+ <p>
+ Administrator may choose to first shutdown the cluster and then downgrade
it.
+ The following are the steps:
+ </p>
+ <ol>
<li>Shutdown all <em>NNs</em> and <em>DNs</em>.</li>
<li>Restore the pre-upgrade release in all machines.</li>
<li>Start <em>NNs</em> with the
"<a href="#namenode_-rollingUpgrade"><code>-rollingUpgrade
downgrade</code></a>" option.</li>
<li>Start <em>DNs</em> normally.</li>
- </ol></li>
- </ul>
-
+ </ol>
</subsection>
+ </section>
- <subsection name="Rollback" id="Rollback">
+ <section name="Rollback" id="Rollback">
<p>
<em>Rollback</em> restores the software back to the pre-upgrade release
but also reverts the user data back to the pre-upgrade state.
@@ -198,6 +251,7 @@
</p>
<p>
Rollback from a newer release to the pre-upgrade release is always
supported.
+ However, it cannot be done in a rolling fashion. It requires cluster
downtime.
Below are the steps for rollback:
</p>
<ul>
@@ -210,7 +264,6 @@
</ol></li>
</ul>
- </subsection>
</section>
<section name="Commands and Startup Options for Rolling Upgrade"
id="dfsadminCommands">
@@ -248,7 +301,7 @@
<p>
Note that the command does not wait for the datanode shutdown to complete.
The "<a href="#dfsadmin_-getDatanodeInfo">dfsadmin -getDatanodeInfo</a>"
- command can be used for checking if the datanode shutdown is complete.
+ command can be used for checking if the datanode shutdown is completed.
</p>
</subsection>
