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HDFS-10910. HDFS Erasure Coding doc should state its currently supported erasure coding policies. Contributed by Yiqun Lin.

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Wei-Chiu Chuang 2016-09-30 12:48:11 -07:00
parent 2ab1ef15c5
commit ee33a02234
1 changed files with 4 additions and 5 deletions
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hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSErasureCoding.md
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@ -59,9 +59,9 @@ Architecture
1. _Read the data from source nodes:_ Input data is read in parallel from source nodes using a dedicated thread pool.
Based on the EC policy, it schedules the read requests to all source targets and reads only the minimum number of input blocks for reconstruction.
1. _Decode the data and generate the output data:_ New data and parity blocks are decoded from the input data. All missing data and parity blocks are decoded together.
2. _Decode the data and generate the output data:_ New data and parity blocks are decoded from the input data. All missing data and parity blocks are decoded together.
1. _Transfer the generated data blocks to target nodes:_ Once decoding is finished, the recovered blocks are transferred to target DataNodes.
3. _Transfer the generated data blocks to target nodes:_ Once decoding is finished, the recovered blocks are transferred to target DataNodes.
* **ErasureCoding policy**
To accommodate heterogeneous workloads, we allow files and directories in an HDFS cluster to have different replication and EC policies.
@ -69,10 +69,9 @@ Architecture
1. _The ECSchema:_ This includes the numbers of data and parity blocks in an EC group (e.g., 6+3), as well as the codec algorithm (e.g., Reed-Solomon).
1. _The size of a striping cell._ This determines the granularity of striped reads and writes, including buffer sizes and encoding work.
2. _The size of a striping cell._ This determines the granularity of striped reads and writes, including buffer sizes and encoding work.
Currently, HDFS supports the Reed-Solomon and XOR erasure coding algorithms. Additional algorithms are planned as future work.
The system default scheme is Reed-Solomon (6, 3) with a cell size of 64KB.
There are three policies currently being supported: RS-DEFAULT-3-2-64k, RS-DEFAULT-6-3-64k and RS-LEGACY-6-3-64k. All with default cell size of 64KB. The system default policy is RS-DEFAULT-6-3-64k which use the default schema RS_6_3_SCHEMA with a cell size of 64KB.
Deployment