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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1218) 20 append: Blocks recovered on startup should be treated with lower priority during block synchronization
Date Tue, 22 Jun 2010 01:58:56 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881012#action_12881012
] 

Todd Lipcon commented on HDFS-1218:
-----------------------------------

right - the block will get truncated to a length *smaller than* the last sync, in the following
not-too-rare circumstance:
1) node loses power
2) node reboots, replays EXT3 journal (almost always results in truncation of replica)
3) lease recovery occurs and includes the rebooted node as a recovery target

> 20 append: Blocks recovered on startup should be treated with lower priority during block
synchronization
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1218
>                 URL: https://issues.apache.org/jira/browse/HDFS-1218
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.20-append
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>             Fix For: 0.20-append
>
>         Attachments: hdfs-1281.txt
>
>
> When a datanode experiences power loss, it can come back up with truncated replicas (due
to local FS journal replay). Those replicas should not be allowed to truncate the block during
block synchronization if there are other replicas from DNs that have _not_ restarted.

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