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Kai Zheng commented on HDFS-7285: --------------------------------- There're some changes in the patch 1 (for codec) that should be placed elsewhere. In {{FSOutputSummer}}, better for 9 (datanode support) {code} + protected DataChecksum getDataChecksum() { + return sum; + } {code} In {{FsShell}}, better for 7 (client side support) {code} + protected String getUsagePrefix() { + return usagePrefix; + } {code} I will continue to look at some other parts. And by the way, I'm going to move left codec issues planned for HDFS-7285 to the follow-on issue since I don't want to interrupt this pre-merge effort. > Erasure Coding Support inside HDFS > ---------------------------------- > > Key: HDFS-7285 > URL: https://issues.apache.org/jira/browse/HDFS-7285 > Project: Hadoop HDFS > Issue Type: New Feature > Reporter: Weihua Jiang > Assignee: Zhe Zhang > Attachments: ECAnalyzer.py, ECParser.py, HDFS-7285-initial-PoC.patch, > HDFS-EC-Merge-PoC-20150624.patch, HDFS-bistriped.patch, > HDFSErasureCodingDesign-20141028.pdf, HDFSErasureCodingDesign-20141217.pdf, > HDFSErasureCodingDesign-20150204.pdf, HDFSErasureCodingDesign-20150206.pdf, > HDFSErasureCodingPhaseITestPlan.pdf, fsimage-analysis-20150105.pdf > > > Erasure Coding (EC) can greatly reduce the storage overhead without sacrifice > of data reliability, comparing to the existing HDFS 3-replica approach. For > example, if we use a 10+4 Reed Solomon coding, we can allow loss of 4 blocks, > with storage overhead only being 40%. This makes EC a quite attractive > alternative for big data storage, particularly for cold data. > Facebook had a related open source project called HDFS-RAID. It used to be > one of the contribute packages in HDFS but had been removed since Hadoop 2.0 > for maintain reason. The drawbacks are: 1) it is on top of HDFS and depends > on MapReduce to do encoding and decoding tasks; 2) it can only be used for > cold files that are intended not to be appended anymore; 3) the pure Java EC > coding implementation is extremely slow in practical use. Due to these, it > might not be a good idea to just bring HDFS-RAID back. > We (Intel and Cloudera) are working on a design to build EC into HDFS that > gets rid of any external dependencies, makes it self-contained and > independently maintained. This design lays the EC feature on the storage type > support and considers compatible with existing HDFS features like caching, > snapshot, encryption, high availability and etc. This design will also > support different EC coding schemes, implementations and policies for > different deployment scenarios. By utilizing advanced libraries (e.g. Intel > ISA-L library), an implementation can greatly improve the performance of EC > encoding/decoding and makes the EC solution even more attractive. We will > post the design document soon. -- This message was sent by Atlassian JIRA (v6.3.4#6332)