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https://issues.apache.org/jira/browse/HDFS-6898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14109922#comment-14109922
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Arpit Agarwal commented on HDFS-6898:
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Thanks for looking at the patch.
I am not sure whether the Linux implementation of {{fallocate}} results in
extra file I/O. However we still have the other issue that Colin mentioned - we
cannot deduce the end of file on restart since our block file format lacks any
header/meta information.
For now we can just "reserve" space for a full block when an RBW block is
created. The "reserved" space is progressively reduced as bytes are ack'ed to
the client. Any remaining space is released when the block is finalized.
[~cmccabe], the attached .03.patch is current.
> 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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