= Hadoop分佈式文件系統使用指南二 =

= 升級 =
 * 由於換版本的話，資料夾內的conf設定檔也勢必被更改，因此目前作法為： 把conf 移至/opt/conf ，hadoop 0.16 與 hadoop 0.18用 ln 做捷徑代換。由於conf已不在hadoop_home內，因此記得匯入conf/hadoop-env.sh
{{{
$ source /opt/conf/hadoop-env.sh
}}}

 * 先看狀態
{{{
$ bin/hadoop dfsadmin -upgradeProgress status

There are no upgrades in progress.
}}}

 * 停止hdfs
   * 注意不可使用bin/stop-all.sh來停止
{{{
$ bin/stop-dfs.sh
}}}

 * 部署新版本的Hadoop
   * 注意每個node的版本都要統一，否則會出現問題


 * 啟動
{{{
$ bin/start-dfs.sh -upgrade
}}}

 * namenode管理網頁會出現升級狀態

= 退回 =

 * 停止集群
{{{
$ bin/stop-dfs.sh
}}}
 * 部署老版本的Hadoop

 * 退回之前版本
{{{
$ bin/start-dfs.sh -rollback
}}}

= 檢查hdfs磁碟狀況 = 
 * fsck 可以
{{{
$ bin/hadoop fsck /

.
/user/waue/input/1.txt:  Under replicated blk_-90085106852013388_1001. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/1.txt:  Under replicated blk_-4027196261436469955_1001. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/2.txt:  Under replicated blk_-2300843106107816641_1002. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/3.txt:  Under replicated blk_-1561577350198661966_1003. Target Replicas is 3 but found 2 replica(s).
.
/user/waue/input/4.txt:  Under replicated blk_1316726598778579026_1004. Target Replicas is 3 but found 2 replica(s).
Status: HEALTHY
 Total size:	143451003 B
 Total dirs:	8
 Total files:	4
 Total blocks (validated):	5 (avg. block size 28690200 B)
 Minimally replicated blocks:	5 (100.0 %)
 Over-replicated blocks:	0 (0.0 %)
 Under-replicated blocks:	5 (100.0 %)
 Mis-replicated blocks:		0 (0.0 %)
 Default replication factor:	3
 Average block replication:	2.0
 Corrupt blocks:		0
 Missing replicas:		5 (50.0 %)
 Number of data-nodes:		2
 Number of racks:		1
The filesystem under path '/' is HEALTHY
}}}

 * 加不同的參數有不同的用處，如
{{{
$ bin/hadoop fsck / -files

/tmp <dir>
/tmp/hadoop <dir>
/tmp/hadoop/hadoop-waue <dir>
/tmp/hadoop/hadoop-waue/mapred <dir>
/tmp/hadoop/hadoop-waue/mapred/system <dir>
/user <dir>
/user/waue <dir>
/user/waue/input <dir>
/user/waue/input/1.txt 115045564 bytes, 2 block(s):  Under replicated blk_-90085106852013388_1001. Target Replicas is 3 but found 2 replica(s).
 Under replicated blk_-4027196261436469955_1001. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/2.txt 987864 bytes, 1 block(s):  Under replicated blk_-2300843106107816641_1002. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/3.txt 1573048 bytes, 1 block(s):  Under replicated blk_-1561577350198661966_1003. Target Replicas is 3 but found 2 replica(s).
/user/waue/input/4.txt 25844527 bytes, 1 block(s):  Under replicated blk_1316726598778579026_1004. Target Replicas is 3 but found 2 replica(s).
Status: HEALTHY
....（同上）
}}}

= Hadoop指令手冊 =
{{{
$ hadoop [--config confdir] [COMMAND] [GENERIC_OPTIONS] [COMMAND_OPTIONS]
}}}

[GENERIC_OPTIONS] :

 || -conf <configuration file>   || 	指定應用程序的配置文件。 || 
 || -D <property=value>  || 	為指定property指定值value。 || 
 || -fs <local|namenode:port>  || 	指定namenode。 || 
 || -jt <local|jobtracker:port>  || 	指定job tracker。只適用於job。 || 


== archieve ==
 * archieve就是把資料壓縮成一個檔案，在壓縮的過程中，還會將被壓縮的目錄結構紀錄在index與masterindex內。
 * 由於每個上傳上去的檔案都被放在一個block中，因此我的input資料夾內共有四個檔，但是每個檔都會佔用一個block，用此方法就可以按照整個打包大小來分配共用去多少個block數。
 * hadoop archive -archiveName name <src>* <dest>
{{{
$ bin/hadoop archive -archiveName foo.har input/* output
09/04/02 14:02:30 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
09/04/02 14:02:30 INFO mapred.JobClient: Running job: job_200904021140_0001
09/04/02 14:02:31 INFO mapred.JobClient:  map 0% reduce 0%
09/04/02 14:02:44 INFO mapred.JobClient:  map 20% reduce 0%
09/04/02 14:02:49 INFO mapred.JobClient:  map 100% reduce 0%
09/04/02 14:02:56 INFO mapred.JobClient: Job complete: job_200904021140_0001
...略
}}}

 * 看har裡面的檔案結構
{{{
$ bin/hadoop dfs -lsr /user/waue/output/foo.har
}}}
 * 看har內檔案的內容
{{{
$ bin/hadoop dfs -cat /user/waue/output/foo.har/part-0
}}}

 * ps: 官方文件介紹的 hadoop dfs -lsr har:///user/hadoop/output/foo.har 會出現錯誤！
{{{
#!sh
lsr: could not get get listing for 'har:/user/waue/output/foo.har/user/waue' : File: har://hdfs-gm1.nchc.org.tw:9000/user/waue/output/foo.har/user/waue/input does not exist in har:///user/waue/output/foo.har

}}}

== distCp ==
 * 是用於大規模集群內部和集群之間拷貝的工具
 * 使用Map/Reduce實現文件分發，錯誤處理和恢復，以及報告生成
 * 舉例為：
{{{
hadoop distcp hdfs://nn1:8020/foo/bar hdfs://nn2:8020/bar/foo
}}}
？？ 然而8020 port 在機器上沒有開，且不是應該檔案會均勻散佈在每個節點上嗎？怎麼還會知道nn1的節點上有這個檔要複製到nn2呢？