Hadoop跨集群迁移数据（整理版）1. 什么是DistCp2. Hadoop DistCp的api使用3. 测试用例4. 应用程序调用distcp接口总结

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我是靠谱客的博主知性雪碧，最近开发中收集的这篇文章主要介绍Hadoop跨集群迁移数据（整理版）1. 什么是DistCp2. Hadoop DistCp的api使用3. 测试用例4. 应用程序调用distcp接口总结，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1. 什么是DistCp

　　DistCp(分布式拷贝)是用于大规模集群内部和集群之间拷贝的工具。它使用Map/Reduce实现文件分发，错误处理和恢复，以及报告生成。它把文件和目录的列表作为map任务的输入，每个任务会完成源列表中部分文件的拷贝。由于使用了Map/Reduce方法，这个工具在语义和执行上都会有特殊的地方。

1.1 DistCp使用的注意事项

　　1. DistCp会尝试着均分需要拷贝的内容，这样每个map拷贝差不多相等大小的内容。但因为文件是最小的拷贝粒度，所以配置增加同时拷贝（如map）的数目不一定会增加实际同时拷贝的数目以及总吞吐量。

　　2. 如果没使用-m选项，DistCp会尝试在调度工作时指定map的数据为 min (total_bytes / bytes.per.map, 20 * num_task_trackers)，其中bytes.per.map默认是256MB。

　　3. 建议对于长时间运行或定期运行的作业，根据源和目标集群大小、拷贝数量大小以及带宽调整map的数目。

　　4. 对于不同Hadoop版本间的拷贝，用户应该使用HftpFileSystem。这是一个只读文件系统，所以DistCp必须运行在目标端集群上（更确切的的说是能够写入目标集群的TaskTracker上）。源的格式是 hftp://<dfs.http.address>/<path> （默认情况dfs.http.address是 <namenode>:50070）。

2. Hadoop DistCp的api使用

[root@node105 ~]# hadoop distcp
usage: distcp OPTIONS [source_path...] <target_path>
OPTIONS
-append
Reuse existing data in target files and
append new data to them if possible
-async
Should distcp execution be blocking
-atomic
Commit all changes or none
-bandwidth <arg>
Specify bandwidth per map in MB
-blocksperchunk <arg>
If set to a positive value, fileswith more
blocks than this value will be split into
chunks of <blocksperchunk> blocks to be
transferred in parallel, and reassembled on
the destination. By default,
<blocksperchunk> is 0 and the files will be
transmitted in their entirety without
splitting. This switch is only applicable
when the source file system implements
getBlockLocations method and the target
file system implements concat method
-copybuffersize <arg>
Size of the copy buffer to use. By default
<copybuffersize> is 8192B.
-delete
Delete from target, files missing in source
-diff <arg>
Use snapshot diff report to identify the
difference between source and target
-f <arg>
List of files that need to be copied
-filelimit <arg>
(Deprecated!) Limit number of files copied
to <= n
-filters <arg>
The path to a file containing a list of
strings for paths to be excluded from the
copy.
-i
Ignore failures during copy
-log <arg>
Folder on DFS where distcp execution logs
are saved
-m <arg>
Max number of concurrent maps to use for
copy
-mapredSslConf <arg>
Configuration for ssl config file, to use
with hftps://. Must be in the classpath.
-numListstatusThreads <arg>
Number of threads to use for building file
listing (max 40).
-overwrite
Choose to overwrite target files
unconditionally, even if they exist.
-p <arg>
preserve status (rbugpcaxt)(replication,
block-size, user, group, permission,
checksum-type, ACL, XATTR, timestamps). If
-p is specified with no <arg>, then
preserves replication, block size, user,
group, permission, checksum type and
timestamps. raw.* xattrs are preserved when
both the source and destination paths are
in the /.reserved/raw hierarchy (HDFS
only). raw.* xattrpreservation is
independent of the -p flag. Refer to the
DistCp documentation for more details.
-rdiff <arg>
Use target snapshot diff report to identify
changes made on target
-sizelimit <arg>
(Deprecated!) Limit number of files copied
to <= n bytes
-skipcrccheck
Whether to skip CRC checks between source
and target paths.
-strategy <arg>
Copy strategy to use. Default is dividing
work based on file sizes
-tmp <arg>
Intermediate work path to be used for
atomic commit
-update
Update target, copying only missingfiles or
directories

3. 测试用例

　　1. 查看将要迁移的目标文件

[root@calculation101 ~]# hdfs dfs -du -h /test/2018/10/

　　2. 创建新集群的测试目录：

[hdfs@node105 root]$
[hdfs@node105 root]$ hdfs dfs -mkdir -p /yangjianqiu/data/
[hdfs@node105 root]$
[hdfs@node105 root]$ hdfs dfs -chown -R root:root
/yangjianqiu/data/
[hdfs@node105 root]$
[hdfs@node105 root]$ exit
exit
[root@node105 ~]#
[root@node105 ~]# hdfs dfs -ls /yangjianqiu
Found 1 items
drwxr-xr-x
- root root
0 2018-10-29 03:29 /yangjianqiu/data

　　2. 开始迁移数据I并记录日志以及迁移数据所用时间：

[root@node105 ~]# mkdir /yangjianqiu
[root@node105 ~]#
[root@node105 ~]#
[root@node105 ~]# nohup time hadoop distcp hdfs://calculation101:8020/test/2018/10/23 hdfs://node105:8020/yangjianqiu/data >> /yangjianqiu/distcp.log 2>&1 & 
[1] 11125 
[root@node105 ~]# 
[root@node105 ~]# jobs 
[1]+ Running nohup time hadoop distcp hdfs://calculation101:8020/test/2018/10/23 hdfs://node105:8020/yangjianqiu/data >> /yangjianqiu/distcp.log 2>&1 &