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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-738) Improve the disk utilization of HDFS
Date Tue, 27 Oct 2009 17:46:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770590#action_12770590
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dhruba borthakur commented on HDFS-738:
---------------------------------------

This module has to account for IO goind on outside of DataNodes. In most cases, mapred.local.dir
is typically on the same device as datanodes. In many other cases, people also write server
logs (GC log) etc to some of these same storage disks. Can this module extract performance
characteristics from the underlying OS?

> 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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