Data Availability
The assurance that data and systems are accessible when needed by authorized users.
Also known as: System availability, High availability, Uptime
Category: Concepts
Tags: security, data, reliability, systems, infrastructure
Explanation
Data availability is the assurance that data and systems are accessible when needed by authorized users. It's one of the three pillars of information security (CIA: Confidentiality, Integrity, Availability). High availability matters because: unavailable data is effectively lost (even temporarily), downtime has real costs (business, safety, productivity), and some data is time-critical (delays reduce value). Threats to availability: hardware failure (disks, servers), software bugs (crashes, corruption), network issues (connectivity loss), attacks (DoS, ransomware), and disasters (fire, flood, power loss). Ensuring availability involves: redundancy (multiple copies, backup systems), fault tolerance (systems continue despite failures), backup and recovery (ability to restore), geographic distribution (survive site-specific disasters), and monitoring (detect and respond to issues). Availability is often measured as 'nines': 99% (3.65 days downtime/year), 99.9% (8.76 hours), 99.99% (52.6 minutes). Higher availability requires exponentially more investment. For knowledge workers, data availability means: ensuring access to information when needed, planning for failures, and balancing availability requirements with cost and complexity.
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