Hadoop集群日常运维
（一）备份namenode的元数据namenode中的元数据非常重要，如丢失或者损坏，则整个系统无法使用。因此应该经常对元数据进行备份，最好是异地备份。1、将元数据复制到远程站点（1）以下代码将secondary namenode中的元数据复制到一个时间命名的目录下，然后通过scp命令远程发送到其它机器 #!/bin/bash export dirname=/mnt/tmphadoop/dfs/namesecondary/current/`date +%y%m%d%H` if [ ! -d ${dirname} ] then mkdir ${dirname} cp /mnt/tmphadoop/dfs/namesecondary/current/* ${dirname} fi scp -r ${dirname} slave1:/mnt/namenode_backup/ rm -r ${dirname} （2）配置crontab，定时执行此项工作0 0,8,14,20 * * * bash /mnt/scripts/namenode_backup_script.sh2、在远程站点中启动一个本地namenode守护进程，尝试加载这些备份文件，以确定是否已经进行了正确备份。（二）数据备份对于重要的数据，不能完全依赖HDFS，而是需要进行备份，注意以下几点（1）尽量异地备份（2）如果使用distcp备份至另一个hdfs集群，则不要使用同一版本的hadoop，避免hadoop自身导致数据出错。（三）文件系统检查定期在整个文件系统上运行HDFS的fsck工具，主动查找丢失或者损坏的块。建议每天执行一次。 [jediael@master ~]$ hadoop fsck / ……省略输出（若有错误，则在此外出现，否则只会出现点，一个点表示一个文件）…… .........Status: HEALTHY Total size: 14466494870 B Total dirs: 502 Total files: 1592 (Files currently being written: 2) Total blocks (validated): 1725 (avg. block size 8386373 B) Minimally replicated blocks: 1725 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 648 (37.565216 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 2 Average block replication: 2.0 Corrupt blocks: 0 Missing replicas: 760 (22.028986 %) Number of data-nodes: 2 Number of racks: 1 FSCK ended at Sun Mar 01 20:17:57 CST 2015 in 608 milliseconds The filesystem under path '/' is HEALTHY （1）若hdfs-site.xml中的dfs.replication设置为3，而实现上只有2个datanode，则在执行fsck时会出现以下错误；/hbase/Mar0109_webpage/59ad1be6884739c29d0624d1d31a56d9/il/43e6cd4dc61b49e2a57adf0c63921c09: Under replicated blk_-4711857142889323098_6221. Target Replicas is 3 but found 2 replica(s).注意，由于原来的dfs.replication为3，后来下线了一台datanode，并将dfs.replication改为2，但原来已创建的文件也会记录dfs.replication为3，从而出现以上错误，并导致 Under-replicated blocks: 648 (37.565216 %)。（2）fsck工具还可以用来检查一个文件包括哪些块，以及这些块分别在哪等 [jediael@master conf]$ hadoop fsck /hbase/Feb2621_webpage/c23aa183c7cb86af27f15d4c2aee2795/s/30bee5fb620b4cd184412c69f70d24a7 -files -blocks -racks FSCK started by jediael from /10.171.29.191 for path /hbase/Feb2621_webpage/c23aa183c7cb86af27f15d4c2aee2795/s/30bee5fb620b4cd184412c69f70d24a7 at Sun Mar 01 20:39:35 CST 2015 /hbase/Feb2621_webpage/c23aa183c7cb86af27f15d4c2aee2795/s/30bee5fb620b4cd184412c69f70d24a7 21507169 bytes, 1 block(s): Under replicated blk_7117944555454804881_3655. Target Replicas is 3 but found 2 replica(s). 0. blk_7117944555454804881_3655 len=21507169 repl=2 [/default-rack/10.171.94.155:50010, /default-rack/10.251.0.197:50010] Status: HEALTHY Total size: 21507169 B Total dirs: 0 Total files: 1 Total blocks (validated): 1 (avg. block size 21507169 B) Minimally replicated blocks: 1 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 1 (100.0 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 2 Average block replication: 2.0 Corrupt blocks: 0 Missing replicas: 1 (50.0 %) Number of data-nodes: 2 Number of racks: 1 FSCK ended at Sun Mar 01 20:39:35 CST 2015 in 0 milliseconds The filesystem under path '/hbase/Feb2621_webpage/c23aa183c7cb86af27f15d4c2aee2795/s/30bee5fb620b4cd184412c69f70d24a7' is HEALTHY 此命令的用法如下： [jediael@master ~]$ hadoop fsck -files Usage: DFSck <path> [-move | -delete | -openforwrite] [-files [-blocks [-locations | -racks]]] <path> start checking from this path -move move corrupted files to /lost+found -delete delete corrupted files -files print out files being checked -openforwrite print out files opened for write -blocks print out block report -locations print out locations for every block -racks print out network topology for data-node locations By default fsck ignores files opened for write, use -openforwrite to report such files. They are usually tagged CORRUPT or HEALTHY depending on their block allocation status Generic options supported are -conf <configuration file> specify an application configuration file -D <property=value> use value for given property -fs <local|namenode:port> specify a namenode -jt <local|jobtracker:port> specify a job tracker -files <comma separated list of files> specify comma separated files to be copied to the map reduce cluster -libjars <comma separated list of jars> specify comma separated jar files to include in the classpath. -archives <comma separated list of archives> specify comma separated archives to be unarchived on the compute machines. The general command line syntax is bin/hadoop command [genericOptions] [commandOptions] 详细解释请见《hadoop权威指南》P376（四）均衡器随时时间推移，各个datanode上的块分布来越来越不均衡，这将降低MR的本地性，导致部分datanode相对更加繁忙。 均衡器是一个hadoop守护进程，它将块从忙碌的DN移动相对空闲的DN，同时坚持块复本放置策略，将复本分散到不同的机器、机架。 建议定期执行均衡器，如每天或者每周。 (1)通过以下命令运行均衡器 [plain]view plaincopy [jediael@masterlog]$start-balancer.sh startingbalancer,loggingto/var/log/hadoop/hadoop-jediael-balancer-master.out 查看日志如下： [plain]view plaincopy [jediael@masterhadoop]$pwd /var/log/hadoop [jediael@masterhadoop]$ls hadoop-jediael-balancer-master.loghadoop-jediael-balancer-master.out [jediael@masterhadoop]$cathadoop-jediael-balancer-master.log 2015-03-0121:08:08,027INFOorg.apache.hadoop.net.NetworkTopology:Addinganewnode:/default-rack/10.251.0.197:50010 2015-03-0121:08:08,028INFOorg.apache.hadoop.net.NetworkTopology:Addinganewnode:/default-rack/10.171.94.155:50010 2015-03-0121:08:08,028INFOorg.apache.hadoop.hdfs.server.balancer.Balancer:0overutilizednodes: 2015-03-0121:08:08,028INFOorg.apache.hadoop.hdfs.server.balancer.Balancer:0underutilizednodes: （2）均衡器将每个DN的使用率与整个集群的使用率接近，这个“接近”是通过-threashold参数指定的，默认是10%。（3）不同节点之间复制数据的带宽是受限的，默认是1MB/s，可以通过hdfs-site.xml文件中的dfs.balance.bandwithPerSec属性指定（单位是字节）。 （五）datanode块扫描器 每个datanode均会运行一个块扫描器，定期检测本节点上的所有块，若发现存在错误（如检验和错误），则通知namenode，然后由namenode发起数据重新创建复本或者修复。 扫描周期由dfs.datanode.scan.period.hours指定，默认为三周（504小时）。 通过地址以下地址查看扫描信息： （1）http://datanote:50075/blockScannerReport 列出总体的检测情况 [plain]view plaincopy TotalBlocks:1919 Verifiedinlasthour:4 Verifiedinlastday:170 Verifiedinlastweek:535 Verifiedinlastfourweeks:535 VerifiedinSCAN_PERIOD:535 Notyetverified:1384 Verifiedsincerestart:559 Scanssincerestart:91 Scanerrorssincerestart:0 Transientscanerrors:0 CurrentscanratelimitKBps:1024 Progressthisperiod:113% Timeleftincurperiod:97.14% （2）http://123.56.92.95:50075/blockScannerReport?listblocks列出所有的块及最新验证状态blk_8482244195562050998_3796 : status : ok type : none scan time : 0 not yet verifiedblk_3985450615149803606_7952 : status : ok type : none scan time : 0 not yet verified尚未验证的情况如上。各字段意义可参考权威指南P379 本文转自 yntmdr 51CTO博客，原文链接：http://blog.51cto.com/yntmdr/1733757，如需转载请自行联系原作者
