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https://issues.apache.org/jira/browse/HDFS-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13838676#comment-13838676
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Konstantin Shvachko commented on HDFS-5590:
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Yes this has always been an "undocumented" parameter.
Deprecating it means adding the respective annotation to the variables and a
deprecation message when the parameter is used in hdfs-site.xml.
Based on the discussion in this jira I see Suresh proposing to change the
default value and Arpit advocating to deprecate.
If you propose to remove the parameter completely then a proper discussion of
such a change would be in line with the tradition.
> Block ID and generation stamp may be reused when persistBlocks is set to false
> ------------------------------------------------------------------------------
>
> Key: HDFS-5590
> URL: https://issues.apache.org/jira/browse/HDFS-5590
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.2.0
> Reporter: Jing Zhao
> Assignee: Jing Zhao
> Attachments: HDFS-5590.000.patch, HDFS-5590.001.patch
>
>
> In a cluster with non-HA setup and dfs.persist.blocks set to false, we may
> have data loss in the following case:
> # client creates file1 and requests a block from NN and get blk_id1_gs1
> # client writes blk_id1_gs1 to DN
> # NN is restarted and because persistBlocks is false, blk_id1_gs1 may not be
> persisted in disk
> # another client creates file2 and NN will allocate a new block using the
> same block id blk_id1_gs1 since block ID and generation stamp are both
> increased sequentially.
> Now we may have two versions (file1 and file2) of the blk_id1_gs1 (same id,
> same gs) in the system. It will case data loss.
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