Re: HDFS / Federated HDFS - Doubts
I have couple of questions about HDFS federation: Can I state different block store directories for each namespace on a datanode ? Can I have some datanodes dedicated to a particular namespace only ? This seems quite interesting. Way to go ! On Tue, Oct 1, 2013 at 9:52 PM, Krishna Kumaar Natarajan natar...@umn.eduwrote: Hi All, While trying to understand federated HDFS in detail I had few doubts and listing them down for your help. 1. In case of *HDFS(without HDFS federation)*, the metadata or the data about the blocks belonging to the files in HDFS is maintained in the main memory of the name node or it is stored on permanent storage of the namenode and is brought in the main memory on demand basis ? [Krishna] Based on my understanding, I assume the entire metadata is in main memory which is an issue by itself. Please correct me if my understanding is wrong. 2. In case of* federated HDFS*, the metadata or the data about the blocks belonging to files in a particular namespace is maintained in the main memory of the namenode or it is stored on the permanent storage of the namenode and is brought in the main memory on demand basis ? 3. Are the metadata information stored in separate cluster nodes(block management layer separation) as discussed in Appendix B of this document ? https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf 4. I would like to know if the following proposals are already implemented in federated HDFS. ( http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability slide-17) - Separation of namespace and block management layers (same as qn.3) - Partial namespace in memory for further scalability - Move partial namespace from one namenode to another Thanks, Krishna
Re: HDFS / Federated HDFS - Doubts
On Wed, Oct 16, 2013 at 9:22 AM, Steve Edison sediso...@gmail.com wrote: I have couple of questions about HDFS federation: Can I state different block store directories for each namespace on a datanode ? No. The main idea of federation was not to physically partition the storage across namespace, but to use all the available storage across the namespaces, to ensure better utilzation. Can I have some datanodes dedicated to a particular namespace only ? As I said earlier, all the datanodes are shared across namespaces. If you want to dedicate datanodes to a particular namespace, you might as well create it as two separate clusters with different set of datanodes and a separate namespace. This seems quite interesting. Way to go ! On Tue, Oct 1, 2013 at 9:52 PM, Krishna Kumaar Natarajan natar...@umn.edu wrote: Hi All, While trying to understand federated HDFS in detail I had few doubts and listing them down for your help. 1. In case of *HDFS(without HDFS federation)*, the metadata or the data about the blocks belonging to the files in HDFS is maintained in the main memory of the name node or it is stored on permanent storage of the namenode and is brought in the main memory on demand basis ? [Krishna] Based on my understanding, I assume the entire metadata is in main memory which is an issue by itself. Please correct me if my understanding is wrong. 2. In case of* federated HDFS*, the metadata or the data about the blocks belonging to files in a particular namespace is maintained in the main memory of the namenode or it is stored on the permanent storage of the namenode and is brought in the main memory on demand basis ? 3. Are the metadata information stored in separate cluster nodes(block management layer separation) as discussed in Appendix B of this document ? https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf 4. I would like to know if the following proposals are already implemented in federated HDFS. ( http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability slide-17) - Separation of namespace and block management layers (same as qn.3) - Partial namespace in memory for further scalability - Move partial namespace from one namenode to another Thanks, Krishna -- http://hortonworks.com/download/ -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
Re: HDFS / Federated HDFS - Doubts
Don't know about question 4 but for the first three -- the metadata is in the memory of the namenode at runtime but is also persisted to disk (otherwise it would be lost if you shut down and re-start the namenode). The copy persisted to disk is on the native file system (not HDFS) and no is not automatically replicated. You have to protect your cluster by backing it up. You not get two issues: 1. The number of files you can store is limited by the amount of memory on the namenode 2. Since all access to files starts with getting the metadata the network I/O lf the namenode is a possible limit Those two issues are solved by splitting the duty across 2 namenodes hence the advantage of federation. [Hopefully someone who knows will tell you about question 4] Cheers Chris On 10/2/2013 12:52 AM, Krishna Kumaar Natarajan wrote: Hi All, While trying to understand federated HDFS in detail I had few doubts and listing them down for your help. 1. In case of *_HDFS(without HDFS federation)_*, the metadata or the data about the blocks belonging to the files in HDFS is maintained in the main memory of the name node or it is stored on permanent storage of the namenode and is brought in the main memory on demand basis ?[Krishna] Based on my understanding, I assume the entire metadata is in main memory which is an issue by itself. Please correct me if my understanding is wrong. 2. In case of*_federated HDFS_*, the metadata or the data about the blocks belonging to files in a particular namespace is maintained in the main memory of the namenode or it is stored on the permanent storage of the namenode and is brought in the main memory on demand basis ? 3. Are the metadata information stored in separate cluster nodes(block management layer separation) as discussed in Appendix B of this document ?https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf 4. I would like to know if the following proposals are already implemented in federated HDFS. (http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability slide-17) * Separation of namespace and block management layers (same as qn.3) * Partial namespace in memory for further scalability * Move partial namespace from one namenode to another Thanks, Krishna
Re: HDFS / Federated HDFS - Doubts
Thanks Chris. Hope someone answers/give pointer to get clear idea about question4. Regards, Krishna On Wed, Oct 2, 2013 at 1:41 PM, Chris Mawata chris.maw...@gmail.com wrote: Don't know about question 4 but for the first three -- the metadata is in the memory of the namenode at runtime but is also persisted to disk (otherwise it would be lost if you shut down and re-start the namenode). The copy persisted to disk is on the native file system (not HDFS) and no is not automatically replicated. You have to protect your cluster by backing it up. You not get two issues: 1. The number of files you can store is limited by the amount of memory on the namenode 2. Since all access to files starts with getting the metadata the network I/O lf the namenode is a possible limit Those two issues are solved by splitting the duty across 2 namenodes hence the advantage of federation. [Hopefully someone who knows will tell you about question 4] Cheers Chris On 10/2/2013 12:52 AM, Krishna Kumaar Natarajan wrote: Hi All, While trying to understand federated HDFS in detail I had few doubts and listing them down for your help. 1. In case of *HDFS(without HDFS federation)*, the metadata or the data about the blocks belonging to the files in HDFS is maintained in the main memory of the name node or it is stored on permanent storage of the namenode and is brought in the main memory on demand basis ? [Krishna] Based on my understanding, I assume the entire metadata is in main memory which is an issue by itself. Please correct me if my understanding is wrong. 2. In case of* federated HDFS*, the metadata or the data about the blocks belonging to files in a particular namespace is maintained in the main memory of the namenode or it is stored on the permanent storage of the namenode and is brought in the main memory on demand basis ? 3. Are the metadata information stored in separate cluster nodes(block management layer separation) as discussed in Appendix B of this document ? https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf 4. I would like to know if the following proposals are already implemented in federated HDFS. ( http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability slide-17) - Separation of namespace and block management layers (same as qn.3) - Partial namespace in memory for further scalability - Move partial namespace from one namenode to another Thanks, Krishna
HDFS / Federated HDFS - Doubts
Hi All, While trying to understand federated HDFS in detail I had few doubts and listing them down for your help. 1. In case of *HDFS(without HDFS federation)*, the metadata or the data about the blocks belonging to the files in HDFS is maintained in the main memory of the name node or it is stored on permanent storage of the namenode and is brought in the main memory on demand basis ? [Krishna] Based on my understanding, I assume the entire metadata is in main memory which is an issue by itself. Please correct me if my understanding is wrong. 2. In case of* federated HDFS*, the metadata or the data about the blocks belonging to files in a particular namespace is maintained in the main memory of the namenode or it is stored on the permanent storage of the namenode and is brought in the main memory on demand basis ? 3. Are the metadata information stored in separate cluster nodes(block management layer separation) as discussed in Appendix B of this document ? https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf 4. I would like to know if the following proposals are already implemented in federated HDFS. ( http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability slide-17) - Separation of namespace and block management layers (same as qn.3) - Partial namespace in memory for further scalability - Move partial namespace from one namenode to another Thanks, Krishna
