The Standby server is the type of server which is brought online when the primary server goes offline, and the application needs continuous availability of the server. The requirement for a mechanism which can shift a primary server to secondary or standby server is always there.
There are three types of standby servers :
* Hot standby : Hot standby method is a method of redundancy in which the primary and secondary backup systems run simultaneously so the data also present in the secondary server in a real-time and this way both systems contain identical information.
* Warm standby : Warm standby is a method of redundancy in which the secondary system runs in the background of the primary system. Data is mirrored in the secondary server at a regular interval, so in this method sometimes both servers don't contain the same data.
* Cold standby : Cold standby is the method of redundancy in which the secondary server is only called when the primary server fails. Cold standby systems are used in cases where data is changed infrequently or for nor critical applications. The physical replacement of Primary server with standby server occurs in cold standby.
