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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6827) Extend the API of NetworkTopology
Date Wed, 01 Sep 2010 13:51:54 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12905027#action_12905027
] 

Steve Loughran commented on HADOOP-6827:
----------------------------------------

I think "racks" confuse people; we have 
# a physical rack topology (which matters for maintenance, power outages, fork-lift truck
related incidents, etc.)
# a network topology (which should really be a hierarchy of switches, some metadata about
cost/throttling on each one, maybe even extend to clusters in the same or separate facilities)
# a power topology which could map from a server name to its UPS Id and perhaps a shared PSU
ID, so you'd know to prefer to replicate content across UPSs and any shared physical PSUs
# HDD batches whose failures may not be independent. 
# Disks inside each server

Really, we should know all these things, so that people can start worrying about them. Currently
everyone discusses "rack awareness" when really it tends to be switch awareness, but once
you start looking at failure modes of a cluster as in HDFS-1094, the differences matter. 

> Extend the API of NetworkTopology
> ---------------------------------
>
>                 Key: HADOOP-6827
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6827
>             Project: Hadoop Common
>          Issue Type: New Feature
>            Reporter: Rodrigo Schmidt
>            Assignee: Rodrigo Schmidt
>
> The current API for NetworkTopology is too restricted (and somehow biased towards the
default block placement algorithm). 
> For instance, it lacks methods to list racks or limit machines within a rack which are
fundamental for HDFS-1094.

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