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Date: Mon, 25 Aug 2014 22:50:59 +0000 (UTC)
From: "Zhe Zhang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12735607.1408579724561.8895.1409007059333@arcas>
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Subject: [jira] [Commented] (HDFS-6898) DN must reserve space for a full
 block when an RBW block is created
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    [ https://issues.apache.org/jira/browse/HDFS-6898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14109909#comment-14109909 ] 

Zhe Zhang commented on HDFS-6898:
---------------------------------

[~cmccabe] Will {{fallocate}} trigger disk I/O? I thought it only manipulates metadata: http://linux.die.net/man/1/fallocate -- "this is done quickly by allocating blocks and marking them as uninitialized, requiring no IO to the data blocks"

> DN must reserve space for a full block when an RBW block is created
> -------------------------------------------------------------------
>
>                 Key: HDFS-6898
>                 URL: https://issues.apache.org/jira/browse/HDFS-6898
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 2.5.0
>            Reporter: Gopal V
>            Assignee: Arpit Agarwal
>         Attachments: HDFS-6898.01.patch, HDFS-6898.03.patch
>
>
> DN will successfully create two RBW blocks on the same volume even if the free space is sufficient for just one full block.
> One or both block writers may subsequently get a DiskOutOfSpace exception. This can be avoided by allocating space up front.


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