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https://issues.apache.org/jira/browse/HDFS-2832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13822352#comment-13822352
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Konstantin Shvachko commented on HDFS-2832:
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> The probability of no collision is P = n!/((n-m)! n^m).
Nicholas, your math is good, as usually. It works well for random events.
My point though is about the deterministic nature of pseudo random sequences.
In the sense that if you initiate two independent PRNGs with the same seed,
they will generate exactly the same sequences.
Sorry for late reply, travelling.
> 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, H2832_20131107.patch,
> editsStored, h2832_20131023.patch, h2832_20131023b.patch,
> h2832_20131025.patch, h2832_20131028.patch, h2832_20131028b.patch,
> h2832_20131029.patch, h2832_20131103.patch, h2832_20131104.patch,
> h2832_20131105.patch, h2832_20131107b.patch, h2832_20131108.patch,
> h2832_20131110.patch, h2832_20131110b.patch, h2832_20131111.patch,
> h2832_20131112.patch, h2832_20131112b.patch
>
>
> 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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