To start database mirroring, you next specify the partners and witness. You need database owner permissions to start and administer a given database mirroring session. On server A, the intended principal server, you tell SQL Server to give a particular database the principal role and what its partner (mirror) server is:
-- Specify the partner from the principal server
ALTER DATABASE [AdventureWorks] SET PARTNER =
N'TCP://B.corp.mycompany.com:5022';
The partner name must be the fully qualified computer name of the partner. Finding fully qualified names can be a challenge, but the Configure Database Mirroring Security Wizard will find them automatically when establishing endpoints.
The fully qualified computer name of each server can also be found running the following from the command prompt:
IPCONFIG /ALL
Concatenate the "Host Name" and "Primary DNS Suffix". If you see something like:
Host Name . . . . . . . . . . . . : A
Primary Dns Suffix . . . . . . . : corp.mycompany.com
Then the computer name is just A.corp.mycompany.com. Prefix 'TCP://' and append ':<port number>' and you then have the partner name.
On the mirror server, you would just repeat the same command, but with the principal server named:
-- Specify the partner from the mirror server
ALTER DATABASE [AdventureWorks] SET PARTNER =
N'TCP://A.corp.mycompany.com:5022';