dragon created HDFS-9963:
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Summary: CLONE - Erasure Coding Support inside HDFS
Key: HDFS-9963
URL: https://issues.apache.org/jira/browse/HDFS-9963
Project: Hadoop HDFS
Issue Type: New Feature
Reporter: dragon
Assignee: Zhe Zhang
Fix For: 3.0.0
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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