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Failover is the ability to switch automatically and seamlessly to a reliable backup system. When a component or primary system fails, either a standby operational mode or redundancy should achieve failover and lessen or eliminate negative impact on users.
To achieve redundancy upon the abnormal failure or termination of a formerly active version, a standby database, system, server, or other hardware component or network must always stand ready to automatically switch into action. In other words, all backup techniques including standby computer server systems must themselves be immune to failure, because failover is critical to disaster recovery (DR).
Virtualization simulates a computer environment using a virtual machine or pseudo machine running host software. In this way, the failover process can be independent of the physical hardware components of computer server systems
Active-active and active-passive or active-standby are the most common configurations for high availability (HA). Each implementation technique achieves failover in a different way, although both improve reliability.
Typically, at least two nodes actively and simultaneously running the same sort of service comprise an active-active high availability cluster. The active-active cluster distributes workloads across all the nodes more evenly, preventing any single node from overloading and achieving load balancing. And because more nodes remain available, throughput and response times improve. To ensure the HA cluster operates seamlessly and achieves redundancy, the individual configurations and settings of the nodes should be identical.
In contrast, in an active-passive cluster, although there must be at least two nodes, not all of them are active. In a two node system with the first node active, the second node will remain passive or on standby as the failover server. In this standby operational mode, it can remain ready should the active, primary server stop functioning to serve as a backup. However, unless there is a failure, clients only connect to the active server.
Just as in the active-active cluster, both servers in the active-standby cluster must be configured with the very same settings. This way, clients cannot perceive any change in service, even if the failover router or server must take over.
Clearly, in an active-standby cluster although the standby node is always running, actual utilization approaches zero.
In an active-active cluster, utilization of both nodes nears half and half— although each node can handle the entire load alone. However, this also means that node failure can cause performance to degrade if one active-active configuration node handles more than half of the load consistently.
Outage time during a failure is virtually zero with an active-active HA configuration, because both paths are active. With an active-passive configuration, outage time has the potential to be greater, as the system must switch from one node to the other, which requires time.
Multi WAN Failover is the ability to move over to other active WAN lines in case of a failure of any of the WAN lines irrespective of the service provider.
Business Operation are hit by power cut to avoid these losses company are looking towards dual WAN failover. Therefore, making use of the proper devices that accomplish multi WAN Failover will definitely improve performance. A combination of connections like T3, DSL, T1, ISDN, Cable or multi connectivity is established, and when they face disruptions there is a need for multi WAN Failover.
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load balancing refers to the process of distributing a set of tasks over a set of resources (computing units), with the aim of making their overall processing more efficient. Load balancing can optimize the response time and avoid unevenly overloading some compute nodes while other compute nodes are left idle.