Re: Copy Vs DistCP
That was a hidden shameless plug Ted ;-) The main disadvantage of fs -cp is that all data has to transit via the machine you issue the command on, depending on the size of data you want to copy that can be a killer. DistCp is distributed as its name imply, so no bottleneck of this kind then. On Apr 14, 2013 6:15 AM, Ted Dunning tdunn...@maprtech.com wrote: Lance, Never say never. Linux programs can read from the right kind of Hadoop cluster without using FUSE. On Fri, Apr 12, 2013 at 10:15 AM, Lance Norskog goks...@gmail.com wrote: Shell 'cp' only works if you use 'fuse', which makes the HDFS file system visible as a Unix mounted file system. Otherwise, Unix programs cannot read or write HDFS files. On 04/11/2013 09:52 AM, KayVajj wrote: Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 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.comwrote: 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.comwrote: 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
Re: Copy Vs DistCP
Inline On Sun, Apr 14, 2013 at 1:13 AM, Mathias Herberts mathias.herbe...@gmail.com wrote: That was a hidden shameless plug Ted ;-) Well, I will admit it was a shameless correction to Lance's absolute and incorrect claim. The main disadvantage of fs -cp is that all data has to transit via the machine you issue the command on, depending on the size of data you want to copy that can be a killer. DistCp is distributed as its name imply, so no bottleneck of this kind then. This is absolutely true. Distcp dominates cp for large copies. On the other hand cp dominates distcp for convenience. In my own experience, I love cp when copying relatively small amounts of data (10's of GB) where the available bandwidth of about a GB/s allows the copy to complete in less time that it takes distcp to get started. At larger sizes (100's of GB and up), the startup time of distcp doesn't matter because once it gets going, it moves data much faster. On Apr 14, 2013 6:15 AM, Ted Dunning tdunn...@maprtech.com wrote: Lance, Never say never. Linux programs can read from the right kind of Hadoop cluster without using FUSE. On Fri, Apr 12, 2013 at 10:15 AM, Lance Norskog goks...@gmail.comwrote: Shell 'cp' only works if you use 'fuse', which makes the HDFS file system visible as a Unix mounted file system. Otherwise, Unix programs cannot read or write HDFS files. On 04/11/2013 09:52 AM, KayVajj wrote: Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 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.comwrote: 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.comwrote: 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
Re: Copy Vs DistCP
This is absolutely true. Distcp dominates cp for large copies. On the other hand cp dominates distcp for convenience. In my own experience, I love cp when copying relatively small amounts of data (10's of GB) where the available bandwidth of about a GB/s allows the copy to complete in less time that it takes distcp to get started. At larger sizes (100's of GB and up), the startup time of distcp doesn't matter because once it gets going, it moves data much faster. Maybe we could put together a 'fs -smartcp' which choses wisely between copy and distcp depending on file size
Re: Copy Vs DistCP
On Sun, Apr 14, 2013 at 10:33 AM, Mathias Herberts mathias.herbe...@gmail.com wrote: This is absolutely true. Distcp dominates cp for large copies. On the other hand cp dominates distcp for convenience. In my own experience, I love cp when copying relatively small amounts of data (10's of GB) where the available bandwidth of about a GB/s allows the copy to complete in less time that it takes distcp to get started. At larger sizes (100's of GB and up), the startup time of distcp doesn't matter because once it gets going, it moves data much faster. Maybe we could put together a 'fs -smartcp' which choses wisely between copy and distcp depending on file size Uh... hmm... This is a good suggestion. Obvious in fact. In retrospect. I would also suggest that the new command be called distcp.
Re: Copy Vs DistCP
Lance, Never say never. Linux programs can read from the right kind of Hadoop cluster without using FUSE. On Fri, Apr 12, 2013 at 10:15 AM, Lance Norskog goks...@gmail.com wrote: Shell 'cp' only works if you use 'fuse', which makes the HDFS file system visible as a Unix mounted file system. Otherwise, Unix programs cannot read or write HDFS files. On 04/11/2013 09:52 AM, KayVajj wrote: Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 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
Re: Copy Vs DistCP
Shell 'cp' only works if you use 'fuse', which makes the HDFS file system visible as a Unix mounted file system. Otherwise, Unix programs cannot read or write HDFS files. On 04/11/2013 09:52 AM, KayVajj wrote: Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com mailto:jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com mailto:apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 PM, Azuryy Yu azury...@gmail.com mailto: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 mailto: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 mailto: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 mailto: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 mailto:vajjalak...@gmail.com *Date:* 2013-04-11 06 tel:2013-04-11%C2%A006:20 *To:* user@hadoop.apache.org mailto: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
Re: Copy Vs DistCP
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
Re: Copy Vs DistCP
yes, you are right. On Thu, Apr 11, 2013 at 3:40 PM, Hemanth Yamijala yhema...@thoughtworks.com wrote: 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
Re: Copy Vs DistCP
Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 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
Re: Copy Vs DistCP
DistCP is prefer for your requirements. On Fri, Apr 12, 2013 at 12:52 AM, KayVajj vajjalak...@gmail.com wrote: Summing up what would be the recommendations for copy 1) DistCP 2) shell cp command 3) Using File System API(FileUtils to be precise) inside of a Java program 4) A MR with an Identity Mapper and no Reducer (may be this is what DistCP does) I did not run any comparisons as my dev cluster is just a two node cluster and not sure how this would perform on a production cluster. Kay On Thu, Apr 11, 2013 at 5:44 AM, Jay Vyas jayunit...@gmail.com wrote: Yes makes sense... cp is serialized and simpler, and does not rely on jobtracker- Whereas distcp actually only submits a job and waits for completion. So it can fail if tasks start to fail or timeout. I Have seen distcp fail and hang before albeit not often. Sent from my iPhone On Apr 10, 2013, at 10:37 PM, Alexander Pivovarov apivova...@gmail.com wrote: if cluster is busy with other jobs distcp will wait for free map slots. Regular cp is more reliable and predictable. Especialy if you need to copy just several GB On Apr 10, 2013 6:31 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
Re: Copy Vs DistCP
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: KayVajjmailto:vajjalak...@gmail.com Date: 2013-04-11 06:20 To: user@hadoop.apache.orgmailto: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
Re: Copy Vs DistCP
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 6:20 PM, KayVajj vajjalak...@gmail.com wrote: 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
Re: Copy Vs DistCP
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
Re: Copy Vs DistCP
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
