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Date: Fri, 4 Nov 2011 07:03:00 +0000 (UTC)
From: "Suresh Srinivas (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HDFS-2535) A Model for Data Durability
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    [ https://issues.apache.org/jira/browse/HDFS-2535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13143792#comment-13143792 ] 

Suresh Srinivas commented on HDFS-2535:
---------------------------------------

Thanks Rob for making the spreadsheet available :-)
                
> 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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