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https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14106386#comment-14106386
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Gopal V commented on HDFS-6581:
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Fair enough, the choice of backing layer should not be enforced by this patch.
In that respect, the huge advantage of this particular approach is that the
HDFS mediatype [RAM] can now refer to both ramfs and tmpfs transparently
according to admin configuration.
As far as tmpfs goes, it was used primarily because HDFS-4949 already has a
hard-dependency on tmpfs for handling short-circuit reads (the skip-checksums
Andrew was talking about is negotiated over tmpfs today).
I found "/dev/shm" references in HDFS code recently and hit issues with that -
filed HDFS-6912, now that I remembered.
> Write to single replica in memory
> ---------------------------------
>
> Key: HDFS-6581
> URL: https://issues.apache.org/jira/browse/HDFS-6581
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: HDFSWriteableReplicasInMemory.pdf
>
>
> Per discussion with the community on HDFS-5851, we will implement writing to
> a single replica in DN memory via DataTransferProtocol.
> This avoids some of the issues with short-circuit writes, which we can
> revisit at a later time.
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