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Date: Mon, 9 Mar 2015 03:04:38 +0000 (UTC)
From: "Ming Ma (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12728965.1406061395000.33962.1425870278334@Atlassian.JIRA>
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Subject: [jira] [Commented] (HDFS-6729) Support maintenance mode for DN
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    [ https://issues.apache.org/jira/browse/HDFS-6729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14352477#comment-14352477 ] 

Ming Ma commented on HDFS-6729:
-------------------------------

Eddy, thanks for the work. We didn't know about this at all until Allen pointed it out HDFS-7877. Sounds like we should combine the effort.

Maybe we can step back and discuss the design. There are couple key things we want to take care of. It will be great if you can check out the design there.

1. Admin interface. Based on our admins input, it seems "dfsadmin -refreshNodes" might be easier to use.
2. DN state machine. We define two new states for maintenance states, ENTERING_MAINTENANCE and IN_MAINTENANCE. It takes care of the case where there are no replicas on other datanodes. It also takes care of different state transition,  decomm states to maintenance states.
3. Block management. We alos enforce the read and write operations when machines are in maintenance states.

Look forward to the collaboration.


> Support maintenance mode for DN
> -------------------------------
>
>                 Key: HDFS-6729
>                 URL: https://issues.apache.org/jira/browse/HDFS-6729
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.5.0
>            Reporter: Lei (Eddy) Xu
>            Assignee: Lei (Eddy) Xu
>         Attachments: HDFS-6729.000.patch, HDFS-6729.001.patch, HDFS-6729.002.patch, HDFS-6729.003.patch, HDFS-6729.004.patch, HDFS-6729.005.patch
>
>
> Some maintenance works (e.g., upgrading RAM or add disks) on DataNode only takes a short amount of time (e.g., 10 minutes). In these cases, the users do not want to report missing blocks on this DN because the DN will be online shortly without data lose. Thus, we need a maintenance mode for a DN so that maintenance work can be carried out on the DN without having to decommission it or the DN being marked as dead.


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