hotspare

A hot spare is a redundant component that is kept powered and ready to take over immediately from a failed component, enabling system operation to continue with minimal interruption. The term is most commonly used in data storage systems and RAID configurations, but can also apply to other components designed for rapid fault recovery.

A hot spare differs from cold and warm spares. A hot spare is already installed, powered, and available for immediate use by the controller. A cold spare is kept offline and requires manual intervention to bring it into service. A warm spare is somewhere in between, typically online but not always ready to assume load without some intervention.

In RAID and enterprise storage, a hot spare is typically a dedicated or global spare disk. When a drive fails, the storage controller automatically begins rebuilding data onto the hot spare using parity or redundancy information. Global spares can be shared among multiple arrays, while dedicated spares are reserved for a specific array.

Advantages of hot spares include reduced downtime, faster recovery after a failure, and improved data availability, which is especially valuable in high-uptime environments. Potential disadvantages include the cost of additional hardware and ongoing power consumption, as well as the risk that multiple simultaneous failures can outpace the rebuild process.

Hot spares are common in data centers, servers, and other environments that rely on RAID, mirroring, or failover strategies. The exact behavior and capabilities depend on the hardware and software, including RAID controller features, rebuild policies, and system monitoring tools.