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https://issues.apache.org/jira/browse/HBASE-13339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14518745#comment-14518745
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Chris Nauroth commented on HBASE-13339:
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[~ndimiduk], thanks for pinging me here. I just want to clarify one thing
about the information that I gave you.
bq. Apparently upgrades are one-way; roll-back from an upgrade in progress is
not supported yet.
This refers to how HDFS supports the use case of returning to the prior
software version, such as if the user discovers an insurmountable bug after the
upgrade has been initiated. We have 2 separate mechanisms to support this.
"Rollback" returns the software to the prior version and also restores the data
to its state when the upgrade was started. (We save a special rollback
checkpoint as soon as the user starts the rolling upgrade progress.) This
process requires downtime.
"Downgrade" returns the software to the prior version and also preserves the
data, including any changes that were made during the upgrade window. This can
be done without downtime.
More details are in the documentation here:
http://hadoop.apache.org/docs/r2.7.0/hadoop-project-dist/hadoop-hdfs/HdfsRollingUpgrade.html#Downgrade_and_Rollback
Rollback from 2.6.0 to 2.4.0 or 2.5.0 is possible. However, downgrade from
2.6.0 to 2.4.0 or 2.5.0 is not possible. I have some work in progress that
will enable support for downgrade in a much wider set of cases. This work
isn't on a jira yet, but I expect to post it in the next week or two. That's
going to be helpful for the future, but this is the current situation for the
versions that you're considering.
I don't know if all of this information is directly relevant to your
discussion, but I wanted to make sure I had given you a clear statement of the
HDFS capabilities.
> Update default Hadoop version to 2.6.0
> --------------------------------------
>
> Key: HBASE-13339
> URL: https://issues.apache.org/jira/browse/HBASE-13339
> Project: HBase
> Issue Type: Bug
> Components: build
> Affects Versions: 2.0.0, 1.1.0
> Reporter: Elliott Clark
> Assignee: Elliott Clark
> Priority: Blocker
> Fix For: 2.0.0, 1.1.0, 1.2.0
>
> Attachments: HBASE-13339-v1.patch, HBASE-13339.patch
>
>
> Current default Hadoop version is getting a little long in the tooth. We
> should update to the latest version. The latest version is backwards
> compatible with 2.5.1's dfs and mr so this should be painless.
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