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https://issues.apache.org/jira/browse/HDFS-9666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15110188#comment-15110188
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Yu Li commented on HDFS-9666:
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bq. However it looked like the benefits of reading from remote RAM were
canceled by the RPC overhead, as compared to short-circuit reads from local disk
Agreed this is true for most *common* case. However, since SATA has much poor
io performance than SSD/RAM, reading from remote SSD/RAM is useful to reduce
spike in the system, or say it's good for reducing the Max latency rather than
Avg. And since there's a switch to turn on/off the feature, user could choose
to use it or not according to different scenarios.
> Enable hdfs-client to read even remote SSD/RAM prior to local disk replica to
> improve random read
> -------------------------------------------------------------------------------------------------
>
> Key: HDFS-9666
> URL: https://issues.apache.org/jira/browse/HDFS-9666
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 2.6.0, 2.7.0
> Reporter: ade
> Assignee: ade
> Fix For: 2.7.2
>
> Attachments: HDFS-9666.0.patch
>
>
> We want to improve random read performance of HDFS for HBase, so enabled the
> heterogeneous storage in our cluster. But there are only ~50% of datanode &
> regionserver hosts with SSD. we can set hfile with only ONE_SSD not ALL_SSD
> storagepolicy and the regionserver on none-SSD host can only read the local
> disk replica . So we developed this feature in hdfs client to read even
> remote SSD/RAM prior to local disk replica.
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