AVAILABILITY Definition & Usage Examples

When you pay for a service or invest in the underlying technology infrastructure, you expect the service to be delivered and accessible at all times, ideally. In the real world of enterprise IT however, ideal service levels are virtually impossible to guarantee. For this reason, organizations evaluate the IT service levels necessary to run business operations smoothly, to ensure minimal disruptions in event of IT service outages.

Networks and software stacks also need to be designed to resist and recover from failures—because they will happen, even in the best of circumstances. Your team should design a system with HA in mind and test functionality before implementation. Once the system is live, the team must frequently test the failover system to ensure it is ready to take over in case of a failure. Our articles on the best server and cloud monitoring tools present a wide selection of solutions worth adding to your tool stack. There is no limit to this number, but going with too many nodes often causes issues with load balancing.

What is reliability, availability and serviceability (RAS)?

Passive redundancy is used to achieve high availability by including enough excess capacity in the design to accommodate a performance decline. The simplest example is a boat with two separate engines driving two separate propellers. The boat continues toward its destination despite failure of a single engine or propeller. A more complex example is multiple redundant power generation facilities within a large system involving electric power transmission.

• One such example is a fire or flood that destroys a data center and its systems when there is no secondary disaster recovery data center.
• Large data center networks power consisting of hundreds of thousands of hardware components.
• When setting up robust production systems, minimizing downtime and service interruptions is often a high priority.
• In general, scheduled downtime is usually the result of some logical, management-initiated event.
• Like all other components in a HA infrastructure, the load balancer also requires redundancy to stop it from becoming a single point of failure.

High availability is a quality of infrastructure design at scale that addresses these latter considerations. Of course, it is critical for systems to be able to handle increased loads and high levels of traffic. But identifying possible failure points and reducing downtime is equally important. This is where a highly available load balancer comes in, for example; it is a scalable infrastructure design that scales as traffic demands increase. Typically this requires a software architecture, which overcomes hardware constraints.. High availability (HA) is a system’s capability to provide services to end users without going down for a specified period of time.

Redundancy is used to create systems with high levels of availability (e.g. aircraft flight computers). In this case it is required to have high levels of failure detectability and avoidance of common cause failures. Availability measures are classified by either the time interval of interest or the mechanisms for the system downtime. If the time interval of interest is the primary concern, we consider instantaneous, limiting, average, and limiting average availability. The aforementioned definitions are developed in Barlow and Proschan [1975], Lie, Hwang, and Tillman [1977], and Nachlas [1998].

More moving parts mean more points of failure, higher redundancy needs, and more challenging failure detection. This article explains the value of maintaining high availability (HA) https://www.globalcloudteam.com/ for mission-critical systems. Read on to learn what availability is, how to measure it, and what best practices your team should adopt to prevent costly service disruptions.

Phrases Containing availability

Availability refers to the percentage of time that the infrastructure, system, or solution remains operational under normal circumstances in order to serve its intended purpose. For cloud infrastructure solutions, availability relates to the time that the data center is accessible or delivers the intend IT service as a proportion of the duration for which the service is purchased. To reduce interruptions and downtime, it is essential to be ready for unexpected events that can bring down servers. At times, emergencies will bring down even the most robust, reliable software and systems. Highly available systems minimize the impact of these events, and can often recover automatically from component or even server failures. Another way to eliminate single points of failure is to rely on geographic redundancy.

Log any variance from the norm and evaluate changes to determine the necessary changes. While load balancing is essential, the process alone is not enough to guarantee high availability. If a balancer only routes the traffic to decrease the load on a single machine, that does not make the entire system highly available. You require a mechanism for detecting errors and acting when one of the components crashes or becomes unavailable. Remove single points of failure by achieving redundancy on every system level.

Modeling and simulation is used to evaluate the theoretical reliability for large systems. The outcome of this kind of model is used to evaluate different design options. A model of the entire system is created, and the model is stressed by removing components. N-1 means the model is stressed by evaluating performance with all possible combinations where one component is faulted. N-2 means the model is stressed by evaluating performance with all possible combinations where two component are faulted simultaneously.

One such example is a fire or flood that destroys a data center and its systems when there is no secondary disaster recovery data center. For example, hospitals and data centers require high availability of their systems to perform routine daily activities. Availability refers to the ability of the user community to obtain a service or good, access the system, whether to submit new work, update or alter existing work, or collect the results of previous work. If a user cannot access the system, it is – from the user’s point of view – unavailable.[1] Generally, the term downtime is used to refer to periods when a system is unavailable.

Two meaningful metrics used in this evaluation are Reliability and Availability. Often mistakenly used interchangeably, both terms have different meanings, serve different purposes, and can incur different cost to maintain desired standards of service levels. High availability systems recover speedily, but they also open up risk in the time it takes for the system to reboot. Fault tolerant systems protect your business against failing equipment, but they are very expensive and do not guard against software failure.

Top-to-bottom or distributed approaches to high availability can both succeed, and hardware or software based techniques to reduce downtime are also effective. High-availability clusters are computers that support critical applications. Specifically, these clusters reliably work together to minimize system downtime.

For example, you can add processing power or more memory to a server by linking it with other servers. Horizontal scaling is a good practice for cloud computing because additional hardware resources can be added to the linked servers with minimal impact. These additional resources can be used to provide redundancy and ensure that your services remain reliable and available.

There are many ways to lose data, or to find it corrupted or inconsistent. Any system that is highly available protects data quality across the board, including during failure events of all kinds. Blockchain is a record-keeping technology designed to make it impossible to hack the system or forge the data stored on it, thereby making it secure and immutable. In practice, vendors commonly express product reliability as a percentage.

While there is overlap between the two terms, availability is not synonymous with uptime. A system may be up and running (uptime) but not available to end users (availability). Whereas HA aims to reduce or remove service downtime, the main goal of DR is to get a disrupted system back to a pre-failure state in case of an incident. Availability is among the first things to consider when setting up a mission-critical IT environment, regardless of whether you install a system on-site or at a third-party data center. High availability lowers the chance of unplanned service downtime and all its negative effects (revenue loss, production delays, customer churn, etc.). To calculate availability of a component or software program, divide the actual operating time by the amount of time it was expected to operate.