Adding Secondary Data Files (ndf)

  • I have a 310GB mdf for my warehouse database. I have just added three more data files to it in order to distribute the data. Now, what do I need to do to ensure data is been written to the new files? What should the size of each new datafile be? Please advice.

  • If they are in the primary filegroup, new data will be automatically written to them. SQL will not however re-balance existing data. Read up on proportional fill for how the data will be distributed.

    As for how big they are, well, how big do they need to be for the future growth of your database?

    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
  • For adding new data files (ndf or mdf) in primary filegroup, application might be gets slow performance due to round robin seraching data from different datafiles. Are you any specific reason for adding new data files?

  • ananda.murugesan (8/30/2012)


    For adding new data files (ndf or mdf) in primary filegroup, application might be gets slow performance due to round robin seraching data from different datafiles.

    Unlikely to be noticeable unless you have lots of files (lots >>> 4) and the data is on disk not in memory

    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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