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https://issues.apache.org/jira/browse/HDFS-7285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14597788#comment-14597788
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Vinayakumar B commented on HDFS-7285:
-------------------------------------
bq. Proposed structure for BlockInfoStriped and BlockInfoUCStriped. It's a
little outdated. Please refer to my github branch for the latest proposed code.
Below are some comments from the updated code from github POC branch, for the
BlockInfo heirarchy.
{code}
+ public abstract StripedBlockStorageOp getStripedBlockStorageOp();
{code}
This need not be in Abstract BlockInfo.java, It is required only for
BlockInfoStriped. All calls done to this is after checking isStriped() only, so
can be casted before calling this.
{code}
@Override
BlockInfoUnderConstruction convertCompleteBlockToUC(
HdfsServerConstants.BlockUCState s, DatanodeStorageInfo[] targets) {
BlockInfoUnderConstructionContiguous ucBlock =
new BlockInfoUnderConstructionContiguous(this,
getBlockCollection().getPreferredBlockReplication(), s, targets);
ucBlock.setBlockCollection(getBlockCollection());
return ucBlock;
}{code}
{{BlockInfoStriped#convertCompleteBlockToUC(..)}} should return
{{BlockInfoUnderConstructionStriped}} instance.
{{StripedBlockStorageOp.java}} needs to have Apache licence header.
> 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-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.
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