HADR - Mirroring

1. Overview

1. Mirroring feature is in maintenance mode and may be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. Use Always On availability groups instead.
2. Database mirroring is a solution for increasing the availability of a SQL Server database. Mirroring is implemented on a per-database basis and works only with databases that use the full recovery model.
3. Committed transactions Mirroring is one of the HA option.
4. Automatic Fail over saves data and downtime (in logshipping manual failover required) .  Data sync are bidirectional.  Witness server is required for Automatic Downtime. 
   
5. Ports are: – Principal Mirroring - 5022, Mirror Mirroring port -  5023, Witness Mirroring Port - 5024 -- EndPoints (in source, in destination and in Witness)
6. Partner Role – Principal and Mirror servers
   

2. Prerequisits

• -For a mirroring session to be established, the partners and the witness, if any, must be running on the same version of SQL Server.
• The database must use the full recovery model. The simple and bulk-logged recovery models do not support database mirroring. Therefore, bulk operations are always fully logged for a mirrored database.
  
• Verify that the mirror server has sufficient disk space for the mirror database.
• When you are creating the mirror database on the mirror server, make sure that you restore the backup of the principal database specifying the same database name WITH NORECOVERY. Also, all log backups that were created after that backup was taken must also be applied, again WITH NORECOVERY.
  
  

3. Terminology

• automatic failover, failover partners, forced service, High-performance mode, manual failover, mirror database, mirror server, principal database, principal server, redo queue, role, role switching, send queue, session, Transaction safety, Witness
  

4. Reference

1. microsoft / Step by step / Manual Failover /