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https://issues.apache.org/jira/browse/HDFS-7866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15183118#comment-15183118
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Walter Su commented on HDFS-7866:
---------------------------------
What do you think let it diverge instead of forcing unification? It takes more
time to understand the new format from the code. I think add some javadoc would
be nice.
How about like this:
{noformat}
/**
* Bit format:
* [4-bit storagePolicyID][12-bit BLOCK_LAYOUT_AND_REDUNDANCY]
* [48-bit preferredBlockSize]
*
* BLOCK_LAYOUT_AND_REDUNDANCY format for replicated block:
* 0 [11-bit replication]
*
* BLOCK_LAYOUT_AND_REDUNDANCY format for striped block:
* 1 [11-bit ErasureCodingPolicy ID]
*
*/
{noformat}
I think getErasureCodingPolicyID() don't have to re-use getReplication(long
header). Even though now they are both 11-bits. In the future,
We might keep split 11-bit ec policy ID. The 2 methods keep diverging. I guess
something like,
{noformat}
/**
* Bit format:
* [4-bit storagePolicyID][12-bit BLOCK_LAYOUT_AND_REDUNDANCY]
* [48-bit preferredBlockSize]
*
* BLOCK_LAYOUT_AND_REDUNDANCY format for non-ec block:
* 0 [11-bit replication]
*
* BLOCK_LAYOUT_AND_REDUNDANCY format for ec striped block:
* 10 [4-bit replication][6-bit ErasureCodingPolicy ID]
*
* BLOCK_LAYOUT_AND_REDUNDANCY format for ec contiguous block:
* 11 [4-bit replication][6-bit ErasureCodingPolicy ID]
*
*/
{noformat}
And I think we should reserve some high-value ID for custom policy. And reserve
some for unknown policy which might intergrated(hard-coded) in the future.
> Erasure coding: NameNode manages multiple erasure coding policies
> -----------------------------------------------------------------
>
> Key: HDFS-7866
> URL: https://issues.apache.org/jira/browse/HDFS-7866
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Kai Zheng
> Assignee: Rui Li
> Attachments: HDFS-7866-v1.patch, HDFS-7866-v2.patch,
> HDFS-7866-v3.patch, HDFS-7866.10.patch, HDFS-7866.11.patch,
> HDFS-7866.12.patch, HDFS-7866.4.patch, HDFS-7866.5.patch, HDFS-7866.6.patch,
> HDFS-7866.7.patch, HDFS-7866.8.patch, HDFS-7866.9.patch
>
>
> This is to extend NameNode to load, list and sync predefine EC schemas in
> authorized and controlled approach. The provided facilities will be used to
> implement DFSAdmin commands so admin can list available EC schemas, then
> could choose some of them for target EC zones.
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