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https://issues.apache.org/jira/browse/HDFS-822?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800947#action_12800947
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Hairong Kuang commented on HDFS-822:
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> if the datanode dies in the middle of a rename, we can have a partial file in
> the destination as well as the complete file in the source, isn't it?
Current code handles this. It removes the partial file in the destination if
rename fails.
Sorry that I did not make my proposal clear. What I am thinking to do in this
jira is to disallow across volume rename. So appending to a block simply moves
the block to the rbw directory in the same volume. This is definitely an
improvement to 0.21 & trunk because 0.21 & trunk may move the block to a
different volume even if the current volume has space. This is a critical bug
that should be fixed. As to whether we should rename across volume when the
current volume is full, lets do it in a different jira.
> Appends to already-finalized blocks can rename across volumes
> -------------------------------------------------------------
>
> Key: HDFS-822
> URL: https://issues.apache.org/jira/browse/HDFS-822
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node
> Affects Versions: 0.21.0, 0.22.0
> Reporter: Todd Lipcon
> Assignee: Hairong Kuang
> Priority: Blocker
> Fix For: 0.21.0, 0.22.0
>
> Attachments: HDFS-822.patch
>
>
> This is a performance thing. As I understand the code in FSDataset.append, if
> the block is already finalized, it needs to move it into the RBW directory so
> it can go back into a "being written" state. This is done using
> volumes.getNextVolume without preference to the volume that the block
> currently exists on. It seems to me that this could cause a lot of slow
> cross-volume copies on applications that periodically
> append/close/append/close a file. Instead, getNextVolume could provide an
> alternate form that gives preference to a particular volume, so the rename
> stays on the same disk.
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