Instant High Availability
This type of solution is common among clusters in the bare metal world, or redundant instances and replicated storage in the virtualized world. By definition, a cluster is a collection of servers that operate as if they are a single machine, with the primary purpose to provide uninterrupted access to the data – even if the server, or application running on the server, loses connectivity or fails completely. With this type of availability solution, there is very little end-user impact as the interruption of service is minimal (even a sub-second in some cases). However, any in-flight data and/or transactions are lost if the system goes down. If your application is stateless, but not load balanced, this is a great solution for you. Instant high availability clusters are commonly used for file sharing and collaboration apps (e.g., email, document management).