[jira] [Commented] (HDFS-5590) Block ID and generation stamp may be reused when persistBlocks is set to false

["Arpit Agarwal (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13837010#comment-13837010 ] 

Arpit Agarwal commented on HDFS-5590:
-------------------------------------

Jing - what do you think of deprecating the setting?

> 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
>
>
> 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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