Database Mirroring is not compatible with FILESTREAM data. By understanding the general known as the MIRROR, made us realize that what we have, will be reflected somewhere else with our permission, in this case are the data. As new terminology, new technology and new capabilities best describe Database Mirroring.
Database Mirroring is also now on proving themselves as a solution that is very essential in an environment of high-level.
Database Mirroring Roles:
Principal Role(mandatory) becomes the source of all transactions in a Database Mirroring session. The principal allows connections, and applications can read data from, write data to it.
Mirror Role(mandatory) is the database partner of principal all the time and constantly receives transactions. Mirror database contains the same data as the principal database.
INFO: Databases in the role of principal and mirror, are exactly equivalent and complete the same with each other, and maintained synchronized with each other.
You cannot configure Database Mirroring if the database are not in the Full recovery model.
Witness server(optional) the role of this witness server is a kind of arbiter to ensure the database that is accessible to a SQL Server instance at a time.
If the primary database fails and witnesses confirm this, the mirror database assumes the primary role and enables data to be available to users. Witness server with a word standing in shadow, only in case of failure, conducts or change roles between principal and mirror.
Database Mirroring can be configured in two different ways. And opportunities based on the conditions that support these options and therefore you decide to choose, but it depends very much on the environment where you want to implement, you should calculate the time of the failure to be as short as possible, the cost of implementation and infrastructure that choice, and location or distance of the primary database and what is thought to be as a mirror.
All these must think and analyze in a very professional way, because mistakes here do not forgiven if we do not have the data safety at any time.
The first option you have is if you want to go in that synchronous mode, or asynchronous mode.nDifference or where to implement these ways which is the best solutions: asynchronous mode is recognized and characterized more as a high performance, while synchronous mode with a very high safety.
This is because the asynchronous mode realizes faster than synchronous mode, but synchronous mode guarantees the same transactions written to it.
When you are hesitant to choose what you want to implement the solution keep in mind not think that is always a right solution for every situation. You should consider the network in which communication is made between server and application.
Also, before starting the Database Mirroring configuration is necessary to restore the backup of the database and all transaction log backup from the primary to secondary.
Database Mirroring operates at the database level, which is not responsible for the objects on the server. Common objects that must transfer are logins, which allow the application to authenticate to the database.
Also you can even have SSIS packages, linked server, SQL Server Agent jobs, error messages, or other objects configured on the server that are hosted in the primary database.
High-Availability solutions as is database mirroring are designed to return your systems online as soon as possible from the primary to secondary(failover), and vice versa(failback).
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