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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1362) Provide volume management functionality for DataNode
Date Tue, 15 Mar 2011 21:06:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1362?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13007187#comment-13007187
] 

Allen Wittenauer commented on HDFS-1362:
----------------------------------------

I look at it like this:

Is there a downside to supporting this functionality?  Just because it is there doesn't mean
one has to use it.  It is trivial to come up with a practical use case (front-side serving
HBase machines).  [I'm avoiding the temptation to make a snide comment about Federation here.
;) ]

It is also worth pointing out that other operating systems have better IO subsystems for hot
swapping.  So while it may not work on one particular config, that doesn't mean all of them
are cursed.

FWIW, RAID-0, mounting, newfs'ing, etc is irrelevant.  If HDFS talked to raw disks this would
matter; Hadoop talks to file systems so any hardware/software OS config would already need
to be in place anyway.  For small grids where you can do replacements, this functionality
makes sense.





> Provide volume management functionality for DataNode
> ----------------------------------------------------
>
>                 Key: HDFS-1362
>                 URL: https://issues.apache.org/jira/browse/HDFS-1362
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node
>    Affects Versions: 0.23.0
>            Reporter: Wang Xu
>            Assignee: Wang Xu
>             Fix For: 0.23.0
>
>         Attachments: DataNode Volume Refreshment in HDFS-1362.pdf, HDFS-1362.4_w7001.txt,
HDFS-1362.5.patch, HDFS-1362.6.patch, HDFS-1362.7.patch, HDFS-1362.txt, Provide_volume_management_for_DN_v1.pdf
>
>
> The current management unit in Hadoop is a node, i.e. if a node failed, it will be kicked
out and all the data on the node will be replicated.
> As almost all SATA controller support hotplug, we add a new command line interface to
datanode, thus it can list, add or remove a volume online, which means we can change a disk
without node decommission. Moreover, if the failed disk still readable and the node has enouth
space, it can migrate data on the disks to other disks in the same node.
> A more detailed design document will be attached.
> The original version in our lab is implemented against 0.20 datanode directly, and is
it better to implemented it in contrib? Or any other suggestion?

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