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Differential backup - Source Information

  • January 26, 2011 at 7:27 am

    #234022

    Dear experts - I have a question regarding differential backup.

    I know that differential backup takes the backup of all the extents that have been modified since last full backup. But, I want to know the source where sqlserver uses or identifies the extents that are eligible for backup.

    I know in oracle there is a metadata table where it maintains all the blocks that have been modified since last complete backup and it make uses of this table while restoring.

    Hope I am clear with my question.

    Thanks,

    Nagarjun.

  • January 26, 2011 at 7:45 am

    #1278473

    There's a type of allocation page called the DCM - the differential change map. It maps which extents have changed since the last full backup. Those extents are the only ones included in the diff backup. A full backup sets the bit to 0 for all extents.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • January 26, 2011 at 6:31 pm

    #1278892

    Here's an interesting article[/url] on predicting the size of a differential backup.

    SQL BAK Explorer - read SQL Server backup file details without SQL Server.
    Supports backup files created with SQL Server 2005 up to SQL Server 2017.

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