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database mirroring witness and client redirect


database mirroring witness and client redirect

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george sibbald
george sibbald
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We are investigating using database mirroring as a DR solution for sharepoint 2010. the sharepoint documentation states that high availability mirroring MUST be used to achieve automatic redirection of the client. However I don't agree with this as I don't believe a witness is required to get the CLIENT to redirect, so high safety would be good enough.

Except in a few blogs I cannot find it definitely stated in MS articles that the witness is not required for client redirect, reading between the lines you would say not, but it goes unstated, so can anyone back me up?

ITs not that I am against a witness per se, its just I want to know what my options are in achieving automated client redirection.

Anyone got feedback on mirroring with SharePoint 2010?

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Lynn Pettis
Lynn Pettis
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george sibbald (5/1/2013)
We are investigating using database mirroring as a DR solution for sharepoint 2010. the sharepoint documentation states that high availability mirroring MUST be used to achieve automatic redirection of the client. However I don't agree with this as I don't believe a witness is required to get the CLIENT to redirect, so high safety would be good enough.

Except in a few blogs I cannot find it definitely stated in MS articles that the witness is not required for client redirect, reading between the lines you would say not, but it goes unstated, so can anyone back me up?

ITs not that I am against a witness per se, its just I want to know what my options are in achieving automated client redirection.

Anyone got feedback on mirroring with SharePoint 2010?


Automatic failover requires the use of a Witness. No witness, your failover option is manual.

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Lynn Pettis

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george sibbald
george sibbald
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Lynn,

agreed - for the databases, thats a no brainer.

but what about the client automatically repointing to the mirror when the principal goes down, thats my question, I see no function for the witness there.

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Lynn Pettis
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george sibbald (5/1/2013)
Lynn,

agreed - for the databases, thats a no brainer.

but what about the client automatically repointing to the mirror when the principal goes down, thats my question, I see no function for the witness there.


If you are talking about the user accessing SharePoint, that user doesn't change where they are looking, they continue to access SharePoint. SharePoint is the application that needs to change from the principal databasee to the mirrored database if the principal goes down or becomes unavailable.

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Lynn Pettis

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george sibbald
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sorry Lynn, thanks for replying but I think you have misunderstood the question: -

a client can use either SQL Server Native Client or .NET Framework Data Provider to connect as long as failover_partner is provided, so as long as the principal and mirror server names are provided in the connection string, as I see it the presence or not of a witness server is irrelevant in allowing the application to redirect following a mirrored database failover - I was just looking for confirmation of that.

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Lynn Pettis
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Something or someone has to tell the mirror database to take over as principal. The application does not do this. If you want SQL Server to automatically failover to the mirror database, you need the Witness. No witness, your only failover option is manual.

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Lynn Pettis

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george sibbald
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Lynn - I would not ask such a newbie question.

I know how the databases fail over, automatically or not, I was just looking for a second opinion on the conditions required for the client to automatically redirect when the database has swapped roles.

I believe the witness is not required for CLIENT redirect - anyone out there have second opinions on that?

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Lynn Pettis
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george sibbald (5/1/2013)
Lynn - I would not ask such a newbie question.

I know how the databases fail over, automatically or not, I was just looking for a second opinion on the conditions required for the client to automatically redirect when the database has swapped roles.

I believe the witness is not required for CLIENT redirect - anyone out there have second opinions on that?


You are correct, the witness is not needed for the client, but it is needed for an automatic failover. The client, in fact, never communicates with the witness.

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Lynn Pettis

For better assistance in answering your questions, click here
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george sibbald
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thank you.

now to convince the sharepoint guys that MS doco can be less than perfect............

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Lynn Pettis
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george sibbald (5/1/2013)
thank you.

now to convince the sharepoint guys that MS doco can be less than perfect............


Yes, looking back at this:


The sharepoint documentation states that high availability mirroring MUST be used to achieve automatic redirection of the client.


Should say something more like this:


... that high availability mirroring MUST be used to achieve automatic failover to the mirror database.


Emphasis is mine.

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Lynn Pettis

For better assistance in answering your questions, click here
For tips to get better help with Performance Problems, click here
For Running Totals and its variations, click here or when working with partitioned tables
For more about Tally Tables, click here
For more about Cross Tabs and Pivots, click here and here
Managing Transaction Logs

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