Blockgerät

Blockgerät is a storage device that provides random access to fixed-size data blocks. It offers a block-level interface to the operating system, in contrast to character devices that expose a byte-oriented stream. Typical examples include hard disk drives, solid-state drives, optical discs, USB mass storage devices, and virtual block devices used in virtualization or software-defined storage.

Key characteristics: Block devices map a contiguous address space to fixed-size blocks (commonly 512 bytes or 4 KiB). I/O operations are performed in block units and can be addressed randomly. The block layer handles buffering, caching, and error recovery; many devices support features such as TRIM/UNMAP for SSDs to optimize space management. Block devices are often partitioned or otherwise divided into logical volumes.

Interface and management: In Unix-like systems, block devices appear as special files under /dev (for example, /dev/sda) and are identified by major/minor numbers. Access occurs through the kernel's block I/O subsystem, which delegates requests to the device driver. I/O supports reads, writes, and various control operations, with performance influenced by I/O schedulers, queue depth, and caching behavior.

Comparison: Block devices differ from character devices, which provide unstructured byte streams without fixed block boundaries. Block devices rely on block-level addressing to ensure random access and data integrity, and some devices can expose both interfaces under different contexts.

Use cases: Block devices serve as the primary medium for persistent storage in operating systems, databases, and file systems, including configurations based on partitions, logical volumes, and virtualized or software-defined storage.