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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2832) Enable support for heterogeneous storages in HDFS
Date Mon, 26 Aug 2013 23:43:56 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13750751#comment-13750751

Andrew Wang commented on HDFS-2832:

bq. I am interested in seeing how the pools abstraction is defined...

I've got a little writeup in the HDFS-4949 design doc, but we're still figuring it out. Arun
expressed interest in reviewing our RM plan, so you could ask him about pools/etc too.

bq. The application must change the Storage Preference on the file to continue.

Is this a stream API? The doc only mentions specifying storage preferences at create time
via {{DFSClient#create}}.

I'm wondering how this works for the case where I write to SSD, run out of capacity, then
want write the rest of my file to HDD. Do I need to close the file, modify the Storage Preference,
then reopen for append? This also potentially requires migrating the last block to HDD, since
storage types are tracked per-block, and then you might hit the "HBase keeps fds open forever"

It'd be nice to see something in the doc discussing the above, under construction replicas
are hard :)

bq. Storage Preferences are not supported on directories. Please let me know if you see anything
in the doc implying otherwise and I will fix it.

Grep for this line: "Storage preferences could be specified per-file or per-directory."
> Enable support for heterogeneous storages in HDFS
> -------------------------------------------------
>                 Key: HDFS-2832
>                 URL: https://issues.apache.org/jira/browse/HDFS-2832
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>    Affects Versions: 0.24.0
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>         Attachments: 20130813-HeterogeneousStorage.pdf
> HDFS currently supports configuration where storages are a list of directories. Typically
each of these directories correspond to a volume with its own file system. All these directories
are homogeneous and therefore identified as a single storage at the namenode. I propose, change
to the current model where Datanode * is a * storage, to Datanode * is a collection * of strorages.

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