按照老赵的博客，由于hadoop没有明确的说明机架感知是感知IP还是感知主机名，所以就都写上了。然后将脚本赋予可执行权限chmod +x RackAware.py，并放到bin/目录下。
然后打开conf/core-site.html
放入一下代码
<property>
<name>topology.script.file.name</name>
<value>/opt/modules/hadoop/hadoop-1.0.3/bin/RackAware.py</value>
<!--机架感知脚本路径-->
</property>
<property>
<name>topology.script.number.args</name>
<value>20</value>
<!--机架服务器数量，由于我写了20个，所以这里写20-->
</property>
然后重启hadoop的namenode和jobtracker，可以在logs里看下namenode和jobtracker的日志，看到机架感知功能已经启用了。
namenode日志
2012-06-08 14:42:19,174 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* NameSystem.registerDatanode: node registration from 192.168.1.49:50010 storage DS-1155827498-192.168.1.49-50010-1338289368956
2012-06-08 14:42:19,204 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack2/192.168.1.49:50010
2012-06-08 14:42:19,205 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* NameSystem.registerDatanode: node registration from 192.168.1.53:50010 storage DS-1773813988-192.168.1.53-50010-1338289405131
2012-06-08 14:42:19,226 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack2/192.168.1.53:50010
2012-06-08 14:42:19,226 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* NameSystem.registerDatanode: node registration from 192.168.1.34:50010 storage DS-2024494948-127.0.0.1-50010-1338289438983
2012-06-08 14:42:19,242 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack1/192.168.1.34:50010
2012-06-08 14:42:19,242 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* NameSystem.registerDatanode: node registration from 192.168.1.54:50010 storage DS-767528606-192.168.1.54-50010-1338289412267
......
2012-06-08 14:42:49,492 INFO org.apache.hadoop.hdfs.StateChange: STATE* Network topology has 2 racks and 10 datanodes
2012-06-08 14:42:49,492 INFO org.apache.hadoop.hdfs.StateChange: STATE* UnderReplicatedBlocks has 0 blocks
2012-06-08 14:42:49,642 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: ReplicateQueue QueueProcessingStatistics: First cycle completed 0 blocks in 0 msec
2012-06-08 14:42:49,642 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: ReplicateQueue QueueProcessingStatistics: Queue flush completed 0 blocks in 0 msec processing time, 0 msec clock time, 1 cycles
jobtracker 日志
2012-06-08 14:50:42,728 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack2/hadoop-node-52
2012-06-08 14:50:42,731 INFO org.apache.hadoop.mapred.JobTracker: Adding tracker tracker_hadoop-node-52:localhost.localdomain/127.0.0.1:33999 to host hadoop-node-52
2012-06-08 14:50:42,753 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack1/hadoop-node-34
2012-06-08 14:50:42,754 INFO org.apache.hadoop.mapred.JobTracker: Adding tracker tracker_hadoop-node-34:localhost.localdomain/127.0.0.1:37025 to host hadoop-node-34
2012-06-08 14:50:42,773 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack2/hadoop-node-51