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https://issues.apache.org/jira/browse/HDFS-5682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14383717#comment-14383717
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Michael Segel commented on HDFS-5682:
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You really can't start looking at this issue until you understand how it will
impact things like scanning.
Before you start trying to define multiple types of storage, you need to first
consider the data flow in and out and what sort of processes occur on the
storage and then for each type of storage, how you would implement it.
As an example... What happens to the data when there's an insert, compaction,
major compaction, indexing (secondary) , etc ... and for each of these
categories how the new storage unit will function.
Looking at the spec, (pdf) this thought process seems to be missing.
> Heterogeneous Storage phase 2 - APIs to expose Storage Types
> ------------------------------------------------------------
>
> Key: HDFS-5682
> URL: https://issues.apache.org/jira/browse/HDFS-5682
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode, namenode
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: 20140522-Heterogeneous-Storages-API.pdf
>
>
> Phase 1 (HDFS-2832) added support to present the DataNode as a collection of
> discrete storages of different types.
> This Jira is to track phase 2 of the Heterogeneous Storage work which
> involves exposing Storage Types to applications and adding Quota Management
> support for administrators.
> This phase will also include tools support for administrators/users.
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