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https://issues.apache.org/jira/browse/HDFS-7994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14490659#comment-14490659
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Hui Zheng commented on HDFS-7994:
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Suppose that there are some blocks using StripedBlockID when namenode loads
fsimage or editlog,so the "hasNonEcBlockUsingStripID" is "true". But after some
time user may delete some or all of these blocks by deleting files. If the
number of these blocks is 0, the "hasNonEcBlockUsingStripID" will become
"false".
> Detect if resevered EC Block ID is already used
> -----------------------------------------------
>
> Key: HDFS-7994
> URL: https://issues.apache.org/jira/browse/HDFS-7994
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Hui Zheng
>
> Since random block IDs were supported by some early version of HDFS, the
> block ID reserved for EC blocks could be already used by some existing blocks
> in a cluster. During NameNode startup, it detects if there are reserved EC
> block IDs used by non-EC blocks. If it is the case, NameNode will do an
> additional blocksMap lookup when there is a miss in a blockGroupsMap lookup.
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