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https://issues.apache.org/jira/browse/HDFS-7285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14593827#comment-14593827
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Zhe Zhang commented on HDFS-7285:
---------------------------------
Since most planned functionalities for this phase is complete, we should
perhaps start examining the entire consolidated patch in preparation for
merging into trunk.
As you might have noticed, there have been a few trunk-based JIRAs trying to
merge generic code refactors to trunk first, so as to minimize the consolidated
patch: HDFS-8487, HDFS-8605, HDFS-8608, HDFS-8623, etc.. I'm working on a PoC
[branch | https://github.com/zhe-thoughts/hadoop/tree/HDFS-EC-Merge] which
rebases HDFS-7285 based on those efforts. I just finished a first pass, which
(I think) includes all the changes except for fsimage/editlog supports.
In particular, the updated {{BlockInfo}} structure from HDFS-8487 will cause
some non-trivial changes to the current HDFS-7285 code (hopefully making it
cleaner). I'm attaching the proposed {{BlockInfoStriped}} and
{{BlockInfoUCStriped}} patch. Comments and suggestions are very welcome.
> 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,
> 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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