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https://issues.apache.org/jira/browse/HDFS-2699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13173399#comment-13173399
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Hari Mankude commented on HDFS-2699:
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One of the issues with inlining checksums (512 bytes of data + 4 byte checksum)
is that it would application layer slower since applications might have to copy
data to get contiguous data only chunks. One of the tradeoff is between
checksum disk iops and application copies on the read side. Similarly, writes
will have to inline checksum bytes in the data stream buffers.
> Store data and checksums together in block file
> -----------------------------------------------
>
> Key: HDFS-2699
> URL: https://issues.apache.org/jira/browse/HDFS-2699
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
>
> The current implementation of HDFS stores the data in one block file and the
> metadata(checksum) in another block file. This means that every read from
> HDFS actually consumes two disk iops, one to the datafile and one to the
> checksum file. This is a major problem for scaling HBase, because HBase is
> usually bottlenecked on the number of random disk iops that the
> storage-hardware offers.
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