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Cloud Computing · Intermediate

Availability Set

Azure logical grouping that spreads VMs across fault domains and update domains within a data center.

Definition

VMs in an availability set are distributed across up to three fault domains (separate power and network) and up to 20 update domains (rebooted separately during planned maintenance; five by default). Availability sets provide a 99.95 percent SLA but do not protect against a data center or zone failure.

Example

Two web VMs in an availability set ensure maintenance reboots never take both offline simultaneously.

Exam tip

Fault domain equals hardware rack failure; update domain equals planned maintenance. Availability zones protect against data center failures.

Related terms