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https://issues.apache.org/jira/browse/HDFS-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13836920#comment-13836920
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Arpit Agarwal commented on HDFS-5590:
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Jing, thanks for reporting this regression with sequential block IDs. I would
go one step further and ask if we can deprecate the setting altogether (and
always persist block allocations)?
> Sequential block ID may cause data loss 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
>
> In a cluster with non-HA setup and dfs.persist.blocks set to false, the
> current sequential block ID mechanism may cause 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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