This article provides examples of using the ‘btrfs device’ command, which is used to manage devices in a btrfs filesystem.

Use case 1: Add one or more devices to a btrfs filesystem

Code:

sudo btrfs device add path/to/block_device1 [path/to/block_device2] path/to/btrfs_filesystem

Motivation: This use case is useful when you want to add one or more physical devices (block devices) to an existing btrfs filesystem.

Explanation:

• sudo btrfs device add: The command to add the specified device(s) to the btrfs filesystem.
• path/to/block_device1 [path/to/block_device2]: The path(s) to the block device(s) that you want to add.
• path/to/btrfs_filesystem: The path to the btrfs filesystem that you want to add the device(s) to.

Example Output:

sudo btrfs device add /dev/sdb1 /dev/sdc1 /mnt/btrfs

Use case 2: Remove a device from a btrfs filesystem

Code:

sudo btrfs device remove path/to/device|device_id [...]

Motivation: Removing a device from a btrfs filesystem is useful when you want to replace or remove a physical device from the filesystem.

Explanation:

• sudo btrfs device remove: The command to remove the specified device from the btrfs filesystem.
• path/to/device|device_id: The path or ID of the device that you want to remove.

Example Output:

sudo btrfs device remove /mnt/btrfs/sdb1

Use case 3: Display error statistics

Code:

sudo btrfs device stats path/to/btrfs_filesystem

Motivation: Displaying error statistics for a btrfs filesystem is helpful for troubleshooting and monitoring the health of the filesystem.

Explanation:

• sudo btrfs device stats: The command to display error statistics for the specified btrfs filesystem.
• path/to/btrfs_filesystem: The path to the btrfs filesystem.

Example Output:

sudo btrfs device stats /mnt/btrfs

Use case 4: Scan all disks and inform the kernel of all detected btrfs filesystems

Code:

sudo btrfs device scan --all-devices

Motivation: This use case is useful when you want to scan all disks and inform the kernel about any detected btrfs filesystems. It ensures that the kernel is aware of the existing btrfs filesystems on the system.

Explanation:

• sudo btrfs device scan: The command to scan disks and inform the kernel about detected btrfs filesystems.
• --all-devices: Optional flag to scan all devices (disks) on the system.

Example Output:

sudo btrfs device scan --all-devices

Use case 5: Display detailed per-disk allocation statistics

Code:

sudo btrfs device usage path/to/btrfs_filesystem

Motivation: Viewing detailed per-disk allocation statistics for a btrfs filesystem provides insights into the disk space usage and allocation of the filesystem.

Explanation:

• sudo btrfs device usage: The command to display per-disk allocation statistics for the specified btrfs filesystem.
• path/to/btrfs_filesystem: The path to the btrfs filesystem.

Example Output:

sudo btrfs device usage /mnt/btrfs

Conclusion:

The ‘btrfs device’ command provides extensive functionality for managing devices in a btrfs filesystem. From adding and removing devices to viewing statistics and scanning disks, this command offers a flexible and powerful set of options for managing and monitoring btrfs filesystems.