%BOOK_ENTITIES; ]> High availability is most commonly a prerequisite characteristic for deployments of application and/or service environments considered critical to an organization's day-to-day operations. The requirement to be able to guarantee service continuity is assigned a certain degree or level and translates into the following technical terms; Service Availability & Performance Data Redundancy & Replication Site Reliability Failover Scenarios This appendix addresses high availability as it applies to the Kolab Groupware environment for using different failure and failover scenarios.

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The term site-reliability applies to complete failover of one or more application and/or service environments serviced from one site during normal operations, to then be serviced from another site upon failover. Different degrees of site-reliability are available. For example, the failover site may have less resources available. Suppose the failover site can make available up to 50% of total processing capacity required for the service to operate at full capacity. The service may show degraded performance, but continues to be generally available. At a lower cost, this scenario still achieves a degree of site-reliability as availability of the service is impacted only for the duration to achieve the complete failover, despite the fact it may be available with significantly degraded performance.

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