Overview
Direct Answer
Block storage is a cloud computing service that presents storage capacity as volumes of fixed-size blocks, each independently mountable to virtual machines as though they were physical hard drives. Unlike object storage, which manages data as complete files, block storage enables low-latency, granular read-write access at the block level.
How It Works
Cloud providers partition storage into logical blocks, typically 4 KB to 64 KB in size, organised into volumes that attach to compute instances over network protocols such as iSCSI or Fibre Channel over Ethernet. The operating system perceives these volumes as direct-attached storage and manages file systems on top of them, allowing standard filesystem operations without awareness of the underlying distributed infrastructure.
Why It Matters
Organisations require this capability for transactional databases, high-performance computing, and applications demanding consistent sub-millisecond latency and IOPS predictability. Block storage enables cost-effective scaling of storage independent of compute capacity whilst maintaining the familiar interface developers and operations teams expect from traditional storage.
Common Applications
Primary use cases include relational databases such as PostgreSQL and MySQL, enterprise resource planning systems, virtualised environments, and boot volumes for cloud instances. Healthcare organisations utilise block storage for imaging systems, whilst financial services employ it for transaction processing where latency and durability are critical.
Key Considerations
Practitioners must account for the performance-cost tradeoff when selecting volume tiers and recognise that block storage incurs per-gigabyte costs regardless of utilisation rates. Additionally, block volumes require explicit backup mechanisms and are bound to specific availability zones, constraining high-availability architecture options.
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