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https://issues.apache.org/jira/browse/HDFS-2699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13171970#comment-13171970
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M. C. Srivas commented on HDFS-2699:
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Couple of observations:
a. If you want to eventually support random-IO, then a block size of 4096 is
too large for the CRC, as it will cause a read-modify-write cycle on the entire
4K. 512-bytes reduces this overhead.
b. Can the value of the variable "io.bytes.per.checksum" be transferred from
the *-site.xml file into the file-properties at the NN at the time of file
creation? If someone messes around with it, old files will still work as before
> 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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