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https://issues.apache.org/jira/browse/HDFS-744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016258#comment-13016258
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dhruba borthakur commented on HDFS-744:
---------------------------------------

We need this functionality for HBase clusters. When HBase writes data to a 
HLog?HFile, it better be persisted on disk, otherwise there could be data loss 
when a non-trivial number of datanodes are power-cycled simultaneously.

> Support hsync in HDFS
> ---------------------
>
>                 Key: HDFS-744
>                 URL: https://issues.apache.org/jira/browse/HDFS-744
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Hairong Kuang
>
> HDFS-731 implements hsync by default as hflush. As descriibed in HADOOP-6313, 
> the real expected semantics should be "flushes out to all replicas and all 
> replicas have done posix fsync equivalent - ie the OS has flushed it to the 
> disk device (but the disk may have it in its cache)." This jira aims to 
> implement the expected behaviour.

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