hdfs haadmin使用，DataNode动态上下线，NameNode状态切换管理，数据块的balance,HA下hdfs-api变化（来自学习资料）

[root@mini2 hadoop-2.6.4]# bin/hdfs haadmin

Usage: DFSHAAdmin [-ns <nameserviceId>]

    [-transitionToActive <serviceId> [--forceactive]]

    [-transitionToStandby <serviceId>]

    [-failover [--forcefence] [--forceactive] <serviceId> <serviceId>]

    [-getServiceState <serviceId>]

    [-checkHealth <serviceId>]

    [-help <command>]

hdfs haadmin -getServiceState nn1

hdfs haadmin –transitionToActive nn1

hdfs haadmin –transitionToStandby nn2

/**

 * 如果访问的是一个ha机制的集群

 * 则一定要把core-site.xml和hdfs-site.xml配置文件放在客户端程序的classpath下

 * 以让客户端能够理解hdfs://ns1/中  “ns1”是一个ha机制中的namenode对——nameservice

 * 以及知道ns1下具体的namenode通信地址

 * @author

 *

 */

public class UploadFile {

         public static void main(String[] args) throws Exception  {

                  Configuration conf = new Configuration();

                  conf.set("fs.defaultFS", "hdfs://ns1/");

                  FileSystem fs = FileSystem.get(new URI("hdfs://ns1/"),conf,"hadoop");

                  fs.copyFromLocalFile(new Path("g:/eclipse-jee-luna-SR1-linux-gtk.tar.gz"), new Path("hdfs://ns1/"));

                  fs.close();

         }

}