lzo   snappy   gzip是hadoop支持的三种压缩方式，目前网上推荐snappy，这里讲解如何安装snappy

1.在linux上安装snappy压缩库

    github上Hadoop源码(https://github.com/apache/hadoop/blob/trunk/BUILDING.txt)推荐的安装方式为：sudo apt-get install snappy libsnappy-dev

 2.编译Hadoop2.7.1源码中模块hadoop-common

        当前Hadoop新的版本在模块hadoop-common中都已经集成了相关压缩库的编解码工具，无需去其它地方下载编解码打包：

        如果之前编译过Hadoop源代码，这一步骤可以不做。

        官网给定的安装包中是不支持snappy压缩的，需要自己重新编译Hadoop源码，而编译源码首先需要保证linux上已经安装了linux关于snappy的库，已经在步骤1中解决。

        关于如何编译Hadoop源代码，请参见http://aperise.iteye.com/blog/2246856

        1.下载hadoop源代码hadoop-2.7.1-src.tar.gz放置于/root下并解压缩 

cd /root
wget http://www.apache.org/dyn/closer.cgi/hadoop/common/hadoop-2.7.1/hadoop-2.7.1-src.tar.gz
tar -zxvf hadoop-2.7.1-src.tar.gz

cd /root/hadoop-2.7.1-src
export MAVEN_OPTS="-Xms256m -Xmx512m"
mvn package -Pdist,native -DskipTests -Dtar -rf :hadoop-common -Drequire.snappy -X
#如果想编译整个代码且单独指定snappy库位置，命令如下：
#mvn package -Pdist,native,docs,src -DskipTests -Drequire.snappy -Dsnappy.lib=/usr/local/lib

3.hadooo中添加snappy支持

#1.将步骤2中编译的snappy支持文件拷贝到Hadoop中
#这里我安装的Hadoop位置为/home/hadoop/hadoop-2.7.1
cp -r /root/hadoop-2.7.1-src/hadoop-dist/target/hadoop-2.7.1/lib/native/* /home/hadoop/hadoop-2.7.1/lib/native/
cp /usr/local/lib/* /home/hadoop/hadoop-2.7.1/lib/native/

#2.将步骤3编译后的hadoop-common-2.7.1.jar文件拷贝到Hadoop
#这里我安装的Hadoop位置为/home/hadoop/hadoop-2.7.1
cp -r /root/hadoop-2.7.1-src/hadoop-dist/target/hadoop-2.7.1/share/hadoop/common/* /home/hadoop/hadoop-2.7.1/share/hadoop/common/ 

#3.修改hadoop的配置文件/home/hadoop/hadoop-2.7.1/etc/hadoop/core-site.xml,增加如下配置：
<property>  
  <name>io.compression.codecs</name>  
  <value>  
  org.apache.hadoop.io.compress.DefaultCodec,  
  org.apache.hadoop.io.compress.GzipCodec,  
  org.apache.hadoop.io.compress.BZip2Codec,   
  org.apache.hadoop.io.compress.Lz4Codec,  
  org.apache.hadoop.io.compress.SnappyCodec  
  </value>  
  <description>A comma-separated list of the compression codec classes that can  
  be used for compression/decompression. In addition to any classes specified  
  with this property (which take precedence), codec classes on the classpath  
  are discovered using a Java ServiceLoader.</description>  
</property> 

#4.修改/home/hadoop/hadoop-2.7.1/etc/hadoop/mapred-site.xml,添加如下内容：
<property>    
  <name>mapreduce.output.fileoutputformat.compress</name>    
  <value>true</value>    
  <description>Should the job outputs be compressed?    
  </description>    
</property>    
<property>    
  <name>mapreduce.output.fileoutputformat.compress.type</name>    
  <value>RECORD</value>    
  <description>If the job outputs are to compressed as SequenceFiles, how should    
               they be compressed? Should be one of NONE, RECORD or BLOCK.    
  </description>    
</property>    
<property>    
  <name>mapreduce.output.fileoutputformat.compress.codec</name>    
  <value>org.apache.hadoop.io.compress.SnappyCodec</value>    
  <description>If the job outputs are compressed, how should they be compressed?    
  </description>    
</property>    
<property>    
  <name>mapreduce.map.output.compress</name>    
  <value>true</value>    
  <description>Should the outputs of the maps be compressed before being    
               sent across the network. Uses SequenceFile compression.    
  </description>    
</property>    
<property>    
  <name>mapreduce.map.output.compress.codec</name>    
  <value>org.apache.hadoop.io.compress.SnappyCodec</value>    
  <description>If the map outputs are compressed, how should they be     
               compressed?    
  </description>    
</property>

    至此，Hadoop中已经可以支持snappy压缩算法了，hbase目前还待配置，请往下看。

4.hbase中添加snappy支持

         至此，hbase中已经添加了对于snappy的支持。

5.在hbase中测试snappy

cd /home/hadoop/hbase-1.2.1/bin/
./hbase org.apache.hadoop.hbase.util.CompressionTest hdfs://hadoop-ha-cluster/hbase/data/default/signal/3a194dcd996fd03c0c26bf3d175caaec/info/0c7f62f10a4c4e548c5ff1c583b0bdfa snappy

      上面hdfs://hadoop-ha-cluster/hbase/data/default/signal/3a194dcd996fd03c0c26bf3d175caaec/info/0c7f62f10a4c4e548c5ff1c583b0bdfa是存在于我Hadoop上的HDFS文件

6.HDFS中如何查看压缩格式为snappy的文件

        hdfs dfs -text /aaa.snappy