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From "Robert Chansler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2535) A Model for Data Durability
Date Wed, 22 Aug 2012 17:50:42 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13439715#comment-13439715

Robert Chansler commented on HDFS-2535:

At Hadoop Summit 2011: http://www.youtube.com/watch?v=zbycDpVWhp0
Also referenced in ;login: February 2012: 
> A Model for Data Durability
> ---------------------------
>                 Key: HDFS-2535
>                 URL: https://issues.apache.org/jira/browse/HDFS-2535
>             Project: Hadoop HDFS
>          Issue Type: Task
>          Components: documentation
>            Reporter: Robert Chansler
>            Assignee: Robert Chansler
>         Attachments: LosingBlocks.xlsx
> This is a statistical model considering data durability in HDFS in the presence of Data
Node failures. The attached spreadsheet considers the probability of losing a block with three
replicas in the case of uncorrelated failures of DNs. Also included is a section that looks
at the consequences of simultaneous failures. 
> The model parameters reflect experience at Yahoo with a large cluster. But it is easy
to change the parameters in the spreadsheet. Number of replicas is not a easily adjusted parameter.
And while published reports (the Google papers) suggest that node failures are not really
uncorrelated, this does give some practical insight into HDFS durability.
> I and others have quoted from this work in the past. I thought it good to make the details
conveniently available.

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