????????
????Hadoop?????????????????????HDFS????????????MR??????????????????MR????????????????????????????????????????MR?????????????HDFS???????е?????????????????????????
????HDFS?????????????????????????????????????????????????????????????????????ext3??????饗block????HDFS??????????ext3????????????????block??block??????????????????HDFS??fsimage???????????????????????????????????????????HDFS???????????????????????????Namenode?????????????Datanode??????Namenode?????????????????????????fsimag????????????????????editlog????Datanode????????????????????Namenode???RPC????????Щ??????????????????ЩDatanode???
????????????????????Namenode????????????????Datanode??????????為????????RPC???????????RPC?????????????IO??audit????????????????????Namenode??????????????HDFS????????????????????????Datanode???????????????????????????????????????????HBase?????????Regionserver??Datanode?????????????????????????????????????Datanode??IO???????й??????????????????????
??????????HDFS?????????????????????????????Щ?????????????????HDFS??????????????????Terasort??Slive??DFSIO??????????????????????????????????????????
???????????
????Terasort
????????????????????????????????????????????????????HDFS????????rpc??????opt??????sync????????????????????Terasort??????????????????????????????????????MR??????????????????Terasortλ??hadoop??example???У???SortBenchmark??http://sortbenchmark.org???????????????????????????Hadoop????IdentityMapper??IdentityReducer??????MR???е?sort????????????partition??????????????

??????????????Terasort???ж?HDFS??????????????????MR????????????????SortBenchmark????μ??????????????????????????????????λ?????????????????ж???HDFS?汾???????????
????Terasort??????????????????teragen????????????????????????terasort???????????????????teravalidate??У??terasort????????????????
???????????teragen??map????block size???????????????????????HDFS?????????????????У?
????hadoop jar hadoop-current/hadoop-0.19.1-dc-examples.jar teragen -Dmapred.map.tasks=100 -Ddfs.block.size=134217728 10000000000 /terasort/output
??????????????/terasort/output??????100??10G??С????????????blocksize??128MB??????????????????????????IO?????????????????????????????????????????????????????teragen???????????????????С???????????????￡?????terasort????????????в??????????????????????????????????????????????????????飬???????????????map???????????????????????terasort??????????????