How to use the command 'raw' (with examples)

The raw command is used in Unix-like operating systems to bind raw character devices to block devices. This enables applications to bypass certain operating system buffering and directly interact with storage hardware, often for performance enhancement or specialized data handling purposes. The command supports binding raw devices, querying existing bindings, and listing all bound raw devices.

Use case 1: Bind a raw character device to a block device

Code:

raw /dev/raw/raw1 /dev/block_device

Motivation:

Binding a raw character device to a block device is crucial in scenarios where an application or a database management system requires low-level access to the disk. This setup allows the application to manage its own buffering and I/O scheduling, resulting in optimized performance suitable for high-demand environments such as transaction-heavy databases.

Explanation:

• raw: This is the command being executed, which manipulates raw bindings.
• /dev/raw/raw1: This specifies the raw character device that you want to bind. Raw devices are designed for applications needing unbuffered access closer to the hardware.
• /dev/block_device: This represents the block device you wish to bind the raw character device to. Block devices, like hard drives, typically communicate with system applications through buffered interactions, which are bypassed here for direct access.

Example output:

/dev/raw/raw1: bound to major 8, minor 0

Use case 2: Query an existing binding instead of setting a new one

Code:

raw /dev/raw/raw1

Motivation:

There are times when system administrators need to check current device configurations or verify the attachment of raw devices to block devices. Querying existing bindings quickly provides this information, ensuring that devices are correctly configured without inadvertently changing bindings.

Explanation:

• raw: The command used to inspect raw bindings.
• /dev/raw/raw1: The specific raw device whose current binding status you wish to query. This device should already be bound to a block device, and the command checks this association.

Example output:

/dev/raw/raw1: bound to major 8, minor 0

Use case 3: Query all bound raw devices

Code:

raw -qa

Motivation:

In complex systems with numerous devices, it is beneficial for system administrators to have a comprehensive overview of all current raw device bindings. This command provides a complete listing of bindings, allowing for thorough auditing and troubleshooting of device configurations across the system.

Explanation:

• raw: The command employed to examine raw bindings.
• -qa: The -q flag stands for ‘query,’ and the -a flag signifies ‘all.’ Together, they instruct the system to present details on all raw device bindings, rather than focusing on an individual device.

Example output:

/dev/raw/raw1: bound to major 8, minor 0
/dev/raw/raw2: bound to major 9, minor 1
/dev/raw/raw3: currently unbound

Conclusion:

The raw command is a valuable tool for managing device bindings on Unix-like systems, particularly when there is a need for unbuffered direct access to block devices. By understanding the specific use cases, such as binding raw devices, checking existing bindings, or listing all bindings, system administrators can ensure optimal performance and configuration of their systems’ storage resources. The examples provided illustrate the utility and application of the raw command in practical scenarios.