Block Device in Linux

In Linux, block devices are a special type of device file that allows users and the system to access and store data in blocks, typically used for hard disk drives, solid-state drives, and other similar storage devices. Block devices are in contrast to character devices (char devices), which transfer data in a character-by-character manner.

Characteristics of Block Devices

• Data Storage and Access in Blocks: Typically, a block is 512 bytes to several kilobytes in size, such as 4KB. When the filesystem writes or reads data, it does so in blocks.
• Random Access: Unlike the sequential access provided by character devices, block devices can randomly access any location in the storage, meaning the system can directly jump to any block address on the storage medium.
• Buffered Operations: Block devices often work with a kernel buffer cache, which can temporarily store input/output data to improve efficiency and performance.

Block Device Files

In the Linux filesystem, block devices are represented as files, usually located in the /dev directory. For example:

• /dev/sda: The first SCSI or SATA hard disk.
• /dev/sdb: The second SCSI or SATA hard disk.
• /dev/nvme0n1: The first NVMe hard disk.

These files represent the entire storage device, but there can also be device files representing individual partitions on the device, such as /dev/sda1 (the first partition on the /dev/sda disk).

Discover block devices in Linux:

• lsblk
• mount
• df -h
• ls /dev/sd*
• cat /proc/partitions
• sudo blkid
• sudo fdisk -l
• sudo parted -l

Interacting with Block Devices

Users and programs typically do not interact directly with block device files, but rather through the abstraction layer provided by filesystems. When formatting, partitioning, or performing low-level operations, tools such as fdisk, mkfs, dd, and others may interact directly with block device files.

Administrative privileges are required to work with block devices, as improper operations can lead to data loss or corruption. When needing to directly access block devices, one should always be very careful to ensure they know what they are doing.

Management of Block Devices

The Linux kernel provides the udev system, which is responsible for managing device nodes and dynamically creating or removing them when devices are added or removed. This allows the system to recognize and configure new hardware without requiring a restart.

Block devices are an integral part of Linux systems, enabling the operating system to interact with physical storage media in an efficient and controlled manner.