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    • Type: Task
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: documentation
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      Description

      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.

        Attachments

        1. LosingBlocks.xlsx
          199 kB
          Robert Chansler

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            • Assignee:
              chansler Robert Chansler
              Reporter:
              chansler Robert Chansler
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