AFAIK, the cp command works fully from the DFS client. It reads bytes from the InputStream created when the file is opened and writes the same to the OutputStream of the file. It does not work at the level of data blocks. A configuration io.file.buffer.size is used as the size of the buffer used in copy - set to 4096 by default.
Thanks Hemanth On Thu, Apr 11, 2013 at 9:42 AM, KayVajj <vajjalak...@gmail.com> wrote: > If CP command is not parallel how does it work for a file partitioned on > various data nodes? > > > On Wed, Apr 10, 2013 at 6:30 PM, Azuryy Yu <azury...@gmail.com> wrote: > >> CP command is not parallel, It's just call FileSystem, even if DFSClient >> has multi threads. >> >> DistCp can work well on the same cluster. >> >> >> On Thu, Apr 11, 2013 at 8:17 AM, KayVajj <vajjalak...@gmail.com> wrote: >> >>> The File System Copy utility copies files byte by byte if I'm not wrong. >>> Could it be possible that the cp command works with blocks and moves them >>> which could be significantly efficient? >>> >>> >>> Also how does the cp command work if the file is distributed on >>> different data nodes?? >>> >>> Thanks >>> Kay >>> >>> >>> On Wed, Apr 10, 2013 at 4:48 PM, Jay Vyas <jayunit...@gmail.com> wrote: >>> >>>> DistCP is a full blown mapreduce job (mapper only, where the mappers do >>>> a "fully" parallel copy to the detsination). >>>> >>>> CP appears (correct me if im wrong) to simply invoke the FileSystem and >>>> issues a copy command for every source file. >>>> >>>> I have an additional question: how is CP which is internal to a cluster >>>> optimized (if at all) ? >>>> >>>> >>>> >>>> On Wed, Apr 10, 2013 at 7:28 PM, 麦树荣 <shurong....@qunar.com> wrote: >>>> >>>>> ** >>>>> Hi， >>>>> >>>>> I think it' better using Copy in the same cluster while using distCP >>>>> between clusters, and cp command is a hadoop internal parallel process and >>>>> will not copy files locally. >>>>> >>>>> ------------------------------ >>>>> 麦树荣 >>>>> >>>>> *From:* KayVajj <vajjalak...@gmail.com> >>>>> *Date:* 2013-04-11 06:20 >>>>> *To:* user@hadoop.apache.org >>>>> *Subject:* Copy Vs DistCP >>>>> I have few questions regarding the usage of DistCP for copying >>>>> files in the same cluster. >>>>> >>>>> >>>>> 1) Which one is better within a same cluster and what factors (like >>>>> file size etc) wouldinfluence the usage of one over te other? >>>>> >>>>> 2) when we run a cp command like below from a client node of the >>>>> cluster (not a data node), How does the cp command work >>>>> i) like an MR job >>>>> ii) copy files locally and then it copy it back at the new >>>>> location. >>>>> >>>>> Example of the copy command >>>>> >>>>> hdfs dfs -cp /<some_location>/file /<new_location>/ >>>>> >>>>> Thanks, your responses are appreciated. >>>>> >>>>> -- Kay >>>>> >>>> >>>> >>>> >>>> -- >>>> Jay Vyas >>>> http://jayunit100.blogspot.com >>>> >>> >>> >> >
