Technical Requirements - System Continuance
More and more enterprises are running mission critical applications that are fundamental to their core business. Failure of those applications can impact user confidence and in some cases can be potentially disastrous to the business. As the data from these applications become increasingly accepted in the large scale and high-end, mission critical parts of the organisation, so the requirements to protect the data through disaster tolerance and business continuance become more and more important.
The goal of building complete solutions in this environment is to ensure that there is no single point of failure. In other words, the loss of a single component cannot cause an application or service to become unavailable. There are many aspects to providing this level of availability, and they can be categorised as:
Storage failures: There are many ways to protect against failure of individual storage devices using techniques such as Redundant Array of Independent Disks (RAID). Storage vendors provide hardware solutions that support many different types of hardware redundancy for storage devices, allowing devices as well as components in the storage controller itself to be swapped out as necessary, without losing access to the critical asset – the data itself.
Network failures: There are many components to a computer network and there are many topologies that provide highly available connectivity. All types of networks need to be considered including the client access networks, the management networks, as well as the storage fabrics (storage area networks) that link the computers to the storage units.
Computer failures: Many enterprise level server platforms provide redundancy inside the computer itself, such as redundant power suppliers and fans. More and more vendors enable 'hot swap' functionality – PCI cards and memory can be swapped in and out without taking the machine out of service. There are also classes of machines that provide fault tolerance by replicating the entire machine and linking multiple CPUs and memory. There are however, occasions where, however much redundancy a machine has, the complete machine will fail or the machine has be taken down for routine maintenance such as upgrading software. In these cases, cluster technologies provide redundancy to enable applications and services to continue automatically.
Site failures: In the most extreme cases, a complete site can fail, either due to a total loss of power, through natural disaster, or due to other issues. More and more organisations are recognising the value of deploying mission critical solutions across multiple geographically dispersed sites. Even without this level of redundancy, it is essential that at as a minimum, effective backup procedures are in place.