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In computing and telecommunications, downtime (also (system) outage or (system) drought colloquially) is a period when a system is unavailable. The unavailability is the proportion of a time-span that a system is unavailable or offline. This is usually a result of the system failure because of an unplanned event, or because of routine maintenance (a planned event).
The terms are commonly applied to networks and servers. The common reasons for unplanned outages are system failures (such as a crash) or communications failures (commonly known as network outage or network drought colloquially). For outages due to issues with general computer systems, the term computer outage (also IT outage or IT drought) can be used.
The term is also commonly applied in industrial environments in relation to failures in industrial production equipment. Some facilities measure the downtime incurred during a work shift, or during a 12- or 24-hour period. Another common practice is to identify each downtime event as having an operational, electrical or mechanical origin.
The opposite of downtime is uptime.
Any on-line testing, performance testing and tuning required should not count towards the outage duration as these activities are typically conducted after the completion of outage or maintenance event and are out of control of most maintenance contractors.
The failures can occur because of damage, failure, design, procedural (improper use by humans), engineering (how to use and deployment), overload (traffic or system resources stressed beyond designed limits), environment (support systems like power and HVAC), (outages designed into the system for a purpose such as software upgrades and equipment growth), other (none of the above but known), or unknown.
The failures can be the responsibility of customer/service provider, vendor/supplier, utility, government, contractor, end customer, public individual, act of nature, other (none of the above but known), or unknown.
Also affected can be the users of an ISP and other customers of a telecommunication network.
Corporations can lose business due to network outage or they may default on a contract, resulting in financial losses. According to Veeam Software 2019 cloud data management report organizations encounter unplanned downtime, on average, 5-10 times per year with the average cost of one hour of downtime being $102,450.
Those people or organizations that are affected by downtime can be more sensitive to particular aspects:
The most demanding users are those that require high availability.
Virtually the entire AT&T network of 4ESS toll tandems switches went in and out of service over and over again on January 15, 1990, disrupting long-distance service for the entire United States. The problem dissipated by itself when traffic slowed down. A software bug was found.
AT&T lost its Frame Relay network for 26 hours on April 13, 1998. This affected many thousands of customers, and bank transactions were one casualty. AT&T failed to meet the service level agreement on their contracts with customers and had to refund 6,600 , costing millions of dollars.
Xbox Live had intermittent downtime during the 2007–2008 holiday season which lasted thirteen days. Increased demand from Xbox 360 purchasers (the largest number of new user sign-ups in the history of Xbox Live) was given as the reason for the downtime; in order to make amends for the service issues, Microsoft offered their users the opportunity to receive a free game.
Sony's PlayStation Network April 2011 outage, began on April 20, 2011, and was gradually restored on May 14, 2011, starting in the United States. This outage is the longest amount of time the PSN has been offline since its inception in 2006. Sony has stated the problem was caused by an external intrusion which resulted in the confiscation of personal information. Sony reported on April 26, 2011, that a large amount of user data had been obtained by the same hack that resulted in the downtime.
Telstra's Ryde switch failed in late 2011 after water egressed into the electrical switch board from continuing wet weather. The Ryde switch is one of the largest by area switches in Australia, and affected more than 720,000 services.
The Miami datacenter of ServerAxis went offline unannounced on February 29, 2016, and was never restored. This impacted multiple providers and hundreds of websites. The outage impacted coverage of the 2016 NCAA Division I women's basketball tournament as WBBState, one of the affected sites, was by far the most comprehensive provider of women's basketball statistics available.
The game platform Roblox had an outage around October 2021, during their Chipotle Event. Many users thought it was because of the event, because it received massive reception, as users could get a free Chipotle burrito during it. The outage was Roblox's longest downtime, lasting 3 days.
On July 8, 2022, Rogers suffered a major nationwide outage in Canada. This simultaneously affected cell phone and internet access, causing 911 calls, interbank transactions to fail and also disrupting government services.
On July 19, 2024, CrowdStrike issued a faulty device driver update for their Falcon software, resulting in Windows PCs, servers, and virtual machines to crash and boot loop. The incident unintentionally affected approximately 8.5 million Windows machines worldwide, including critical infrastructure such as 911 services in various states. It is considered to be the largest outage in the history of information technology.
For Internet servers downtimes above 1% per year or worse can be regarded as unacceptable as this means a downtime of more than 3 days per year. For e-commerce and other industrial use any value above 0.1% is usually considered unacceptable.
A process needs to be in place to detect a malfunction - network monitoring - and to restore the network to a working condition - this generally involves a help desk team that can troubleshoot a problem, one composed of trained engineers; a separate help desk team is usually necessary in order to field user input, which can be particularly demanding during a downtime.
A network management system can be used to detect faulty or degrading components prior to customer complaints, with proactive fault rectification.
Risk management techniques can be used to determine the impact of network outages on an organisation and what actions may be required to minimise risk. Risk may be minimised by using reliable components, by performing maintenance, such as upgrades, by using redundant systems or by having a contingency plan or business continuity plan. Technical means can reduce errors with error correcting codes, retransmission, redundancy check, or diversity scheme.
One of the biggest causes of downtime is misconfiguration, where a planned change goes wrong. Typically organisations rely on manual effort to manage the process of configuration backups, but this requires highly skilled engineers with the time to manage the process across a multi-vendor network. Automation tools are available to manage backups, but there are very few solutions that handle configuration recovery which is needed to minimize the overall impact of the outage.
Outages can also be planned as a result of a predictable natural event, such as Sun outage.
Maintenance downtimes have to be carefully scheduled in industries that rely on computer systems. In many cases, system-wide downtimes can be averted using what is called a "rolling upgrade" - the process of incrementally taking down parts of the system for upgrade, without affecting the overall functionality.
Downtime is also generalized in a personal sense, being used to refer to a period of sleep or recreation.
This term is used also in factories or industrial use. See total productive maintenance (TPM).
A notable example is that of Downdetector, an online website owned by Ookla which tracks regular downtime and major outages with user outage reports made in the site, which also includes the page for each website on Downdetector itself and Twitter. It is currently available in 45 countries (with a different site in each country), and tracks 12,000 services internationally.
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