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https://issues.apache.org/jira/browse/HDFS-7788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14642823#comment-14642823
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Sangjin Lee commented on HDFS-7788:
-----------------------------------
The backport to 2.6.0 is pretty trivial but the test FS image needs to be
recreated for 2.6.0. Also it'd be good to rename the variable
(HADOOP_2_7_ZER0_BLOCK_SIZE_TGZ) in TestFSImage for 2.6.
I'll post a suggested backport patch for 2.6.0.
> Post-2.6 namenode may not start up with an image containing inodes created
> with an old release.
> -----------------------------------------------------------------------------------------------
>
> Key: HDFS-7788
> URL: https://issues.apache.org/jira/browse/HDFS-7788
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Kihwal Lee
> Assignee: Rushabh S Shah
> Priority: Blocker
> Labels: 2.6.1-candidate
> Fix For: 2.7.0
>
> Attachments: HDFS-7788-binary.patch, rushabh.patch
>
>
> Before HDFS-4305, which was fixed in 2.1.0-beta, clients could specify
> arbitrarily small preferred block size for a file including 0. This was
> normally done by faulty clients or failed creates, but it was possible.
> Until 2.5, reading a fsimage containing inodes with 0 byte preferred block
> size was allowed. So if a fsimage contained such an inode, the namenode would
> come up fine. In 2.6, the preferred block size is required be > 0. Because
> of this change, the image that worked with 2.5 may not work with 2.6.
> If a cluster ran a version of hadoop earlier than 2.1.0-beta before, it is
> under this risk even if it worked fine with 2.5.
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