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From "Hong Tang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-738) Improve the disk utilization of HDFS
Date Tue, 27 Oct 2009 07:18:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770408#action_12770408
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Hong Tang commented on HDFS-738:
--------------------------------

+1 on the direction.

I have been brewing the idea that we should have a shared io load monitor, publishing the
load (using util% or queue size) through shared memory, and allow task processes to use the
same info to decide which disk to write to.

> Improve the disk utilization of HDFS
> ------------------------------------
>
>                 Key: HDFS-738
>                 URL: https://issues.apache.org/jira/browse/HDFS-738
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>            Reporter: Zheng Shao
>
> HDFS data node currently assigns writers to disks randomly. This is good if there are
a large number of readers/writers on a single data node, but might create a lot of contentions
if there are only 4 readers/writers on a 4-disk node.
> A better way is to introduce a base class DiskHandler, for registering all disk operations
(read/write), as well as getting the best disk for writing new blocks. A good strategy of
the DiskHandler would be to distribute the load of the writes to the disks with more free
spaces as well as less recent activities. There can be many strategies.
> This could help improve the HDFS multi-threaded write throughput a lot - we are seeing
<25MB/s/disk on a 4-disk/node 4-node cluster (replication is already considered) given
8 concurrent writers (24 writers considering replication). I believe we can improve that to
2x.

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