Availability refers to the degree of reliability with which information in an IT system can be accessed. If a system is set up in a high availability configuration, then it is also highly dependable.
Downtime can quickly lead to financial losses for an organization. The goal of High Availability (HA) is to provide access to the information in a database at any given time, regardless of server failure.
There is a common misconception that high availability is a single software feature or hardware component. It is not so much a hardware component or a single piece of software as it is a system design. For a system to have high availability, it utilizes multiple servers connected to a Storage Area Network (SAN). The servers provide redundancy (e.g., when one server fails, another takes control), while the SAN provides storage capacity.
The diagram below depicts two servers in a basic high availability configuration:
Two servers in a basic high availability configuration
Enterprise applications such as Microsoft Exchange, Microsoft Dynamics CRM and SyteLine ERP run on a server constantly communicating with the databases in real time. High availability is achieved by enabling more than one server to communicate with the database and seamlessly fail over in case of hardware malfunction. The more servers present in an HA configuration, the higher the system reliability, and the lower the risk of system outages.
If a high availability setup is not utilized, then each critical component becomes a single point of failure and the entire system will be offline until the issue is identified, and parts are ordered, delivered, and installed. The same equipment failure would not affect a high availability system, because at the instant the failure occurs, it will fail over to another node in the cluster.
To illustrate this, imagine a 747 Jumbo Jet. If one of the engines has to be shut down, the plane will still fly with three engines because of its extra engine capacity.
While the chance of a server having a failure is low, in the real world, things do go wrong and a system-down event can trigger a domino effect capable of bringing business to a standstill. Any amount of downtime can be highly detrimental to a company’s bottom line. The higher the availability for a certain system, the smaller the chance there will be a downtime, making the system more reliable.
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