Database Mirroring

Database Mirroring

Mirroring was intorduce in 2005 by Microsoft. It is a low cost low maintenance solution when I say low maintenance it only means it has degree less complex than the cluster. In Mirroring, Principal database is duplicated exactly to a Mirror which is clear from its name.

Let consider pros and cons for which some people like mirroring and some don't.

Pros:
1. It easy to implement.
2. It can ensure no data loss (if using High Safety mode)
3.It provides a secure copy of database separate from the production so if production goes down Mirror database kicks in immediately without using time for manual restoration.
4.it provide three modes of operations. Asynchronous , Synchronous without witness ,Synchronous with witness.

Cons:
Most people think Mirror Server is actually a waste of resource. Reason because it waiting for principal server to die malfunction  or gone for maintenance and then it can start. It something more then standby server and database.

Asynchronous : Principal database commit data without waiting for mirror database to commit. Data loss chance present.

Synchronous without witness : Principal database does not commit data before the mirror database. Therefore principal database waits for mirror database to commit first. No Data loss. Manual fail over to Mirror Database

Synchronous with witness:Principal database does not commit data before the mirror database. Therefore principal database waits for mirror database to commit first. No Data loss. Automatic fail over to Mirror Database.

Implementation of mirror Server will be discussed in the next and above will be linked with the post.