In the IT world, business continuity is everything. The availability of resources is paramount to ensuring that streamlined IT operations are carried out seamlessly. This is what high availability tries to guarantee. But what exactly is high availability? This article will define the concept and outline the factors that make high availability beneficial for IT teams and organizations.
What is high availability?
High availability refers to the state of a system, element, component, or anything related to continuously operating without interruption. This concept aims to deliver optimal and quality performance throughout a specific given time, ensuring business continuity and minimal downtime.
What are high availability systems (HA systems)?
High availability systems (HA systems) refer to systems that employ various techniques and strategies to achieve high availability in a given environment. High availability systems comprise vital components that work together to ensure uninterrupted service delivery. They are:
- Redundancy – High availability systems enforce redundancy by having backup systems or components that can take over if the primary system suffers from system failure.
- Failover – Failover factor refers to the process of transferring all functions to a redundant system in instances when the primary system cannot function or becomes unavailable.
- Fault tolerance – High-availability systems should have fault tolerance to guarantee continuous operations despite hardware or software unavailability caused by system failures.
- Load balancing – Load balancing is the ability of high-availability systems to distribute workloads to prevent overload that may lead to disruptive failure. This also promotes system efficiency, ensuring that workloads are distributed in a way that doesn’t strain system resources.
- Uptime – Uptime refers to the percentage of time a system is operational and available for use. It dictates the effectiveness of high-availability systems.
How is high availability measured?
High availability is measured by essential metrics and key performance indicators (KPIs) that show the efficiency of a high availability system.
1. High availability metrics (HA metrics)
High availability metrics are raw data points that measure a system’s performance and efficiency, providing essential context for quantifying how a system operates and responds to various conditions. HA metrics are as follows:
- Uptime percentage. A measurement that expresses a system’s availability based on the percentage of time it is accessible and operational.
- Mean Time Between Failures (MTBF). This pertains to the average time a system spends unavailable due to system failure.
- Mean Time To Repair (MTTR). This metric measures the average time it takes to fix a system failure and get it up and running again.
- Response time. A measurement that dictates how fast a system responds to a request.
- Throughput. Measures the number of transactions a system can process in a given time.
- Resource utilization. This metric measures how efficiently system resources are utilized.
- Error rate. This pertains to the measurement that shows how frequently errors are occurring.
- Data loss. This metric refers to the quantitative amount of data lost during a system failure.
2. High Availability Key Performance Indicators (HA KPIs)
Derived from metrics, high availability Key Performance Indicators (HA KPIs) are measurements that align with an organization’s goals, providing actionable insights that can be used to dictate the following actions an organization must take to optimize system performance and achieve business objectives. Here are some vital elements of HA KPIs:
- Service Level Agreements (SLAs). These are contractual service-level customer commitments.
- Customer Satisfaction. This measurement refers to the satisfaction level of the system’s end-users (customers) with its overall performance.
- Recovery Time Objective (RTO). RTO, or Recovery Time Objective, is a measurement that expresses the maximum allowable downtime for a system, limiting an acceptable duration for which a system can be unavailable due to service interruption.
- Recovery Point Objective (RPO). This KPI defines the maximum amount of data loss that can be tolerated due to system failure.
Quantification of high availability
High availability is often quantified using a “nines“ system to represent the uptime percentage. Each “nine” added to the number means a higher level of reliability, expressing less downtime potential. Here’s a breakdown:
- Two nines (99%): The system is available for 99% of the year, which equates to about 3.65 days of downtime.
- Three nines (99.9%): This level indicates 99.9% uptime or about 8.76 hours of downtime annually.
- Four nines (99.99%): This represents 99.99% uptime, translating to approximately 52.6 minutes of downtime annually.
- Five nines (99.999%): This is a very high level of availability, allowing for only about 5.26 minutes of downtime annually.
- Six nines (99.9999%): An extremely high standard, with just 31.5 seconds of downtime permitted annually.
Strategies for ensuring high availability
Enforcing high availability on systems entails essential techniques for maximum efficiency. Here are some strategies that can help with achieving system resiliency, reliability, and continuous operations:
1. Clustering and load balancing
While clustering is a strategy that groups servers into a single system to maximize fault tolerance and scalability, load balancing distributes incoming traffic across multiple servers. It helps maintain a system’s optimal performance by preventing system overload and improving response time.
2. Redundancy strategies
These techniques include hardware redundancy or duplication of physical system components, software redundancy or the usage of multiple software instances in disruptive malfunctions, and data redundancy, which refers to the creation of multiple copies of data to reduce the risks of data loss.
3. Failover mechanisms
These strategies deal with switchovers or transfers of functions to a working system in case the primary system is unavailable. Failover mechanisms include manual failover, where switching the system to a backup is done manually, requiring human intervention, and automatic failover, where the transfer of operations to standby systems happens automatically.
Other strategies under this mechanism are planned failover, where scheduled switching to another system is enforced, and unplanned failover, which triggers a switch to backup.
4. Disaster recovery and business continuity
These two strategies work together to prevent operational failures and workflow interventions. Disaster recovery allows systems to restore resources after a damaging incident, improving data loss prevention. Meanwhile, business continuity techniques enable business functions to continue during and after system disruptions.
5. Data replication and backup
Lastly, data replication and backup protect organizations from losing critical data. This is done by creating copies of important data as backups that are easily retrievable in case of data compromise or loss. These data can be stored in multiple locations for redundancy and accessibility.
What are the challenges of maintaining high availability?
IT teams tasked to employ and maintain high availability to systems may encounter hiccups in implementing, managing, and optimizing redundant systems and processes. Here are some of the challenges they might come across:
- Complexity. From setting up a system to maintaining its high availability, IT teams may be faced with complex undertakings, making it hard to design, implement, and manage HA systems.
- Cost. Setting up a high-availability system may incur skyrocketing costs for organizations. In addition to the costly setup due to expensive hardware and software, tasks such as testing, maintenance, management, and anything that requires someone to operate and monitor the system may increase upfront and ongoing costs.
- Human error. Inevitable instances like human error can become a challenge, especially when system configuration, maintenance, or troubleshooting is erroneous.
- Impact on performance. High-availability system setups are also susceptible to performance issues. They can introduce challenges that may involve latency or overhead, affecting system performance.
The importance of high availability
Maintaining high availability is paramount to business continuity and effective crisis management. Its value in retrospect to organizational goals is indispensable because it can prevent impactful instances such as performance throttling, data loss, and disruptive downtime. While maintaining high availability may be challenging due to some factors, aiming to achieve its main purposes will surely help promote operational excellence, customer satisfaction, and overall business success.
