[jira] Created: (HDFS-903) NN should verify images and edit logs on startup

["Eli Collins (JIRA)" <ji...@apache.org>]

NN should verify images and edit logs on startup
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                 Key: HDFS-903
                 URL: https://issues.apache.org/jira/browse/HDFS-903
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: name-node
            Reporter: Eli Collins
            Assignee: Eli Collins
            Priority: Critical


I was playing around with corrupting fsimage and edits logs when there are multiple dfs.name.dirs specified. I noticed that:
 * As long as your corruption does not make the image invalid, eg changes an opcode so it's an invalid opcode HDFS doesn't notice and happily uses a corrupt image or applies the corrupt edit.
* If the first image in dfs.name.dir is "valid" it replaces the other copies in the other name.dirs, even if they are different, with this first image, ie if the first image is actually invalid/old/corrupt metadata than you've lost your valid metadata, which can result in data loss if the namenode garbage collects blocks that it thinks are no longer used.

How about we maintain a checksum as part of the image and edit log and check those on startup and refuse to startup if they are different. Or at least provide a configuration option to do so if people are worried about the overhead of maintaining checksums of these files. Even if we assume dfs.name.dir is reliable storage this guards against operator errors.

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[jira] Resolved: (HDFS-903) NN should verify images and edit logs on startup

["Hairong Kuang (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-903?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hairong Kuang resolved HDFS-903.
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      Resolution: Fixed
    Release Note: Store fsimage MD5 checksum in VERSION file. Validate checksum when loading a fsimage. Layout version bumped.
    Hadoop Flags: [Incompatible change, Reviewed]

I've just committed this!

> NN should verify images and edit logs on startup
> ------------------------------------------------
>
>                 Key: HDFS-903
>                 URL: https://issues.apache.org/jira/browse/HDFS-903
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>            Reporter: Eli Collins
>            Assignee: Hairong Kuang
>            Priority: Critical
>             Fix For: 0.22.0
>
>         Attachments: trunkChecksumImage.patch, trunkChecksumImage1.patch, trunkChecksumImage2.patch, trunkChecksumImage3.patch, trunkChecksumImage4.patch
>
>
> I was playing around with corrupting fsimage and edits logs when there are multiple dfs.name.dirs specified. I noticed that:
>  * As long as your corruption does not make the image invalid, eg changes an opcode so it's an invalid opcode HDFS doesn't notice and happily uses a corrupt image or applies the corrupt edit.
> * If the first image in dfs.name.dir is "valid" it replaces the other copies in the other name.dirs, even if they are different, with this first image, ie if the first image is actually invalid/old/corrupt metadata than you've lost your valid metadata, which can result in data loss if the namenode garbage collects blocks that it thinks are no longer used.
> How about we maintain a checksum as part of the image and edit log and check those on startup and refuse to startup if they are different. Or at least provide a configuration option to do so if people are worried about the overhead of maintaining checksums of these files. Even if we assume dfs.name.dir is reliable storage this guards against operator errors.

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