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I was wondering if there is any information on what scenarios might cause a DB Mirror to have to be recreated?

I am attempting to research how sturdy the technology is and under what scenarios do we have to proceed with caution such as long running maintenance tasks or large bulk transactions.

Thanks,

Matt

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2 Answers 2

Situations that come to mind are:

  • Having to Restore the Primary due to a bad code release / user error
  • Loss of Network Connectivity for extended periods of time or due to maintenance activities
  • DNS Issues / Misconfiguration of Aliases in SQL Server Configuration Manager

Microsoft also has quite a bit of information in an article appropriately named "Possible Failures During Database Mirroring"

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Thanks for the link, dont think I have come across that page before. –  Lima Mar 30 '11 at 11:43

A few scenarios are explored in this case study. Generally you would need to recreate a mirror in the event of:

  • Catastrophic failure of the physical hardware on which it resides
  • A break in connectivity long enough for it to fall too far behind the primary

Of course, the same planning applies in the case of needing to recreate the primary from the mirror! It is a matter of your own topology whether your strategy for recovery is to go to the mirror, or to tape.

Often when making major changes, at my site we will pause database mirrors (or the Oracle equivalent, defer log shipping) until we are happy, then resume it. This gives us a measure of protection against things going hatstand for any reason, including operator error, problems wth new code, etc.

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So when pausing a Mirror, how would you deal with transaction log file growth? I am guessing that you cant take backups of transaction log files and truncate, so would you then have to balance available disk space with the duration of the pause? –  Lima Mar 30 '11 at 11:41
    
Yes, you would need to have sufficient space. In practice, we usually pause between 1 and 4 hours, just long enough to cover the work behing done and tested, at the quietest possible time anyway. –  Gaius Mar 30 '11 at 11:57

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