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

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

Answer 1

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

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

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Answer 2

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

Answer 3

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

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Sean Gallardy | Blog | Twitter

Answer 4

Thanks for your answer.

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

regards