Pages and Extents

  • Can SQL Server Engine write or retrieve from disk only a single page or is an extent retrieved/fully allocated regardless? This question came up when a very knowledgeable friend of mine told me that because the SQL Engine usually caches an entire extend and allocates extents regardless it's good practice to always format storage with 64KB block sizes. In my thought process, if the SQL engine is able to only write or retrieve a single page (without caching/allocating an extent) then there are scenarios where that wouldn't improve performance.

  • Yes it can, and that knowledgable friend is wrong, 64kb is not the ideal block size, SQL does not read and write in extents only.

    http://blog.purestorage.com/what-is-sql-servers-io-block-size/

    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

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