July 8, 2009 at 9:57 am
Hi,
Just a couple of questions about SQL2005 Database mirroring:
1). For the purpose of creating an OFF site DR, is it safe not to have the witness throughout the setup?
2). Are transactions streamed to the mirror from the principle once hardened to disk in that no transaction log exists – there is a permanent open connection between the principal and the mirror through which transactions are streamed?
Thanks in advance
Russell Morgan
July 8, 2009 at 10:29 am
Hi Russell,
Welcome to the forums.
Regarding your first point, in my opinion it depends on what you mean by “safe”. Given that this is to be a DR site I will assume that you require ALL of your data to be available at the DR site, in the event of a failure at the primary site.
To accommodate this scenario you would need, in my opinion, to use the “High Protection” mode as this does not require a “Witness” server and also provides “FULL” Transaction Safety i.e. transactions must be hardened at both the Principal and Mirror.
With regard to point two, how transactions are handled between two servers participating in Database Mirroring, this is determined by the Transaction Safety mode, which in turn is determined by the Operating Mode for the Database Mirroring configuration.
I suggest reading the following good overview of Database Mirroring:
http://technet.microsoft.com/en-us/library/cc917680.aspx
Hope this helps.
July 10, 2009 at 3:12 am
Russell,
If you want to manually failover in the case of any contingency then need not to create witness .Else for automatic failover witness is needed .
For your second question , the communication is done through the Service broker via contracts , queues and messages .
Regards
Abhay Chaudhary
Sr.DBA (MCITP/MCTS :SQL Server 2005/2008 ,OCP 9i)
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