Storage Fundamentals

Storage is the part of a computer system that retains data and makes it available again. The useful unit is not a disk or an array but a storage service: an interface, a path to media, a namespace, performance behavior, failure boundaries, and a recovery plan.

An application issues a read or write through a block, file, or object interface. Operating-system and storage software translate that request, move it through controllers or a network, and place the data on media. Caches may acknowledge a write before it reaches its final medium, while metadata records where the data belongs. Every layer can change latency, durability, and failure behavior.

Three access models

Block storage exposes numbered blocks and normally leaves partitioning and file systems to the host. File storage exposes named files and directories through a shared file service. Object storage exposes objects, metadata, and identifiers through an API. The access model determines which side owns the namespace and which applications can use the service.