假如设备链接层次分3层，第一层交换机d1下面连多个交换机rk1,rk2,rk3,rk4,…. 每个交换机对应一个机架。

d1(rk1(hs11,hs12,…),rk2(hs21,hs22,…), rk3(hs31,hs32,…),rk4(hs41,hs42,…),…)

可以用程序或脚本完成由host到设备的映射。比如，用python，生成一个topology.py：

然后在core-site.xml中配置
<property>
<name>topology.script.file.name</name>
<value>/home/hadoop/hadoop-1.1.2/conf/topology.py</value>
<description> The script name that should be invoked to resolve DNS names to
NetworkTopology names. Example: the script would take host.foo.bar as an
argument, and return /rack1 as the output.
</description>
</property>

python机架脚本：

[hadoop@hs11 conf]$ cat topology.py
#!/usr/bin/env python

”’
This script used by hadoop to determine network/rack topology. It
should be specified in hadoop-site.xml via topology.script.file.name
Property.
topology.script.file.name
/home/hadoop/hadoop-1.1.2/conf/topology.py

To generate dict:
for i in range(xx):
#print “\”hs%d\”:\”/rk%d/hs%d\”,”%(i,(i-1)/10,i)

print “\”hs%d\”:\”/rk%d\”,”%(i,(i-1)/10)

Andy 2013.7.23
”’

import sys
from string import join

DEFAULT_RACK = ‘/rk0′;

RACK_MAP = {
“hs11″:”/rk1″,
“hs12″:”/rk1″,
“hs13″:”/rk1″,
“hs14″:”/rk1″,
“hs15″:”/rk1″,
“hs16″:”/rk1″,
“hs17″:”/rk1″,
“hs18″:”/rk1″,
“hs19″:”/rk1″,
“hs20″:”/rk1″,
“hs21″:”/rk2″,
“hs22″:”/rk2″,
“hs23″:”/rk2″,
“hs24″:”/rk2″,
“hs25″:”/rk2″,
“hs26″:”/rk2″,
“hs27″:”/rk2″,
“hs28″:”/rk2″,
“hs29″:”/rk2″,
“hs30″:”/rk2″,
“hs31″:”/rk3″,
“hs32″:”/rk3″,
“hs33″:”/rk3″,
“hs34″:”/rk3″,
“hs35″:”/rk3″,
“hs36″:”/rk3″,
“hs37″:”/rk3″,
“hs38″:”/rk3″,
“hs39″:”/rk3″,
“hs40″:”/rk3″,
“hs41″:”/rk4″,
“hs42″:”/rk4″,
“hs43″:”/rk4″,
“hs44″:”/rk4″,
“hs45″:”/rk4″,
“hs46″:”/rk4″,

…

“10.10.20.11″:”/rk1″,
“10.10.20.12″:”/rk1″,
“10.10.20.13″:”/rk1″,
“10.10.20.14″:”/rk1″,
“10.10.20.15″:”/rk1″,
“10.10.20.16″:”/rk1″,
“10.10.20.17″:”/rk1″,
“10.10.20.18″:”/rk1″,
“10.10.20.19″:”/rk1″,
“10.10.20.20″:”/rk1″,
“10.10.20.21″:”/rk2″,
“10.10.20.22″:”/rk2″,
“10.10.20.23″:”/rk2″,
“10.10.20.24″:”/rk2″,
“10.10.20.25″:”/rk2″,
“10.10.20.26″:”/rk2″,
“10.10.20.27″:”/rk2″,
“10.10.20.28″:”/rk2″,
“10.10.20.29″:”/rk2″,
“10.10.20.30″:”/rk2″,
“10.10.20.31″:”/rk3″,
“10.10.20.32″:”/rk3″,
“10.10.20.33″:”/rk3″,
“10.10.20.34″:”/rk3″,
“10.10.20.35″:”/rk3″,
“10.10.20.36″:”/rk3″,
“10.10.20.37″:”/rk3″,
“10.10.20.38″:”/rk3″,
“10.10.20.39″:”/rk3″,
“10.10.20.40″:”/rk3″,
“10.10.20.41″:”/rk4″,
“10.10.20.42″:”/rk4″,
“10.10.20.43″:”/rk4″,
“10.10.20.44″:”/rk4″,
“10.10.20.45″:”/rk4″,
“10.10.20.46″:”/rk4″,

…
}

if len(sys.argv)==1:
print DEFAULT_RACK
else:
print join([RACK_MAP.get(i, DEFAULT_RACK) for i in sys.argv[1:]],” “)

原来这个程序我返回的是

“hs11″:”/rk1/hs11″,

结果执行mapreduce程序时报如下错误：