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Question about database mirroring with "high-safety mode without automatic failover" RRS feed

  • Question

  • Hi,

    In the database mirroring, I understand the "possible data loss" with high-performance mode(asynchronous).

    But I don't understand why we can have "possible data loss" with high-safety mode when principal server is lost ?
    In high-safety mode, transaction committed on the principal are also committed on the mirror.


    ref: http://msdn.microsoft.com/en-us/library/ms179344(d=printer,v=sql.105).aspx

    Do you have an idea ?
    best regards
    David

    Monday, January 14, 2013 1:54 PM

Answers

All replies

  • Read this article http://msdn.microsoft.com/en-us/library/ms189977(v=sql.105).aspx

    Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

    MS SQL optimization: MS SQL Development and Optimization
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    Monday, January 14, 2013 3:01 PM
  • Yes, I read it.

    But I still understand why ?

    principal do not applied change on datafile until it's write in transaction log of the mirror.

    So, if principal crashed, the transaction not written to the mirror will be rollback on the old principal when it will come back.

    So the data will not be lost because they will not be applied on old principal.

    missing something ?

    regards,

    David

    Monday, January 14, 2013 6:41 PM
  • David,

    You're assuming that the mirroring session is always 'synchronized' but in the case of what you're asking, it happens - as stated in the article - that this is only possible during the 'synchronizing' state. This is possible as the mirror was synchronizing but not yet synchronized when a forced failover occurs.

    -Sean


    Sean Gallardy | Blog | Twitter


    • Proposed as answer by retracementMVP Tuesday, January 15, 2013 1:56 PM
    • Marked as answer by Maggie Luo Tuesday, January 22, 2013 8:29 AM
    • Edited by Maggie Luo Tuesday, January 22, 2013 8:30 AM mark as answer
    Monday, January 14, 2013 8:15 PM
    Answerer
  • Thanks for your answer.

    This article(mirror,mirror) explain that:http://technet.microsoft.com/en-us/magazine/hh334997.aspx

    regards


    • Marked as answer by Maggie Luo Tuesday, January 22, 2013 8:29 AM
    • Edited by Maggie Luo Tuesday, January 22, 2013 8:30 AM mark as answer
    Tuesday, January 15, 2013 4:15 PM