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

Bcachefs is a modern filesystem that combines the superior scalability of a new-generation filesystem with integrated caching capabilities. It provides efficient data management strategies by allowing the combination of SSDs and HDDs to maximize both performance and storage capacity. Bcachefs is designed with robust data integrity and fault tolerance features and can be employed in various use cases, such as multi-device configurations and enhanced storage management setups.

Use case 1: Format a partition with bcachefs

Code:

sudo bcachefs format path/to/partition

Motivation: The first step in utilizing a new storage device or partition is to format it with a filesystem. Formatting a partition with bcachefs prepares it to handle data in a structured manner, allowing the operating system and users to read and write files efficiently. By using bcachefs, one can take advantage of its enhanced features such as resilience and performance improvements over traditional filesystems.

Explanation:

• sudo: This command requires administrative privileges to access hardware at a low level.
• bcachefs format: The format subcommand initializes the specified partition with the bcachefs filesystem.
• path/to/partition: This is the location of the storage device or partition to be formatted. It should be replaced with the actual path.

Example Output:

Formatting device /dev/sdx...
Filesystem formatted successfully with bcachefs.

Use case 2: Mount a bcachefs filesystem

Code:

sudo bcachefs mount path/to/partition path/to/mountpoint

Motivation: Once a partition is formatted with bcachefs, the next logical step is mounting it so it can be accessed by the system and users. Mounting a filesystem enables it to be part of the system’s directory tree, making it possible to store and retrieve data within it as if it was part of the main filesystem.

Explanation:

• sudo: Necessary for granting permission to modify system-level settings.
• bcachefs mount: The mount subcommand attaches the specified filesystem to your directory tree.
• path/to/partition: Specifies which partition to mount.
• path/to/mountpoint: Indicates where in the file hierarchy the filesystem should be mounted. This should be a directory that already exists.

Example Output:

Mounting /dev/sdx to /mnt/mybcachefs
Filesystem mounted successfully.

Use case 3: Create a RAID 0 filesystem where an SSD acts as a cache and an HDD acts as a long-term storage

Code:

sudo bcachefs format --label=ssd.ssd1 path/to/ssd/partition --label=hdd.hdd1 path/to/hdd/partition --replicas=1 --foreground_target=ssd --promote_target=ssd --background_target=hdd

Motivation: Combining an SSD and HDD in a RAID 0 configuration using bcachefs is desirable for users needing both high performance and large storage capacity. The SSD acts as a cache to speed up access to frequently accessed files, while the HDD provides long-term storage, balancing speed and capacity efficiently.

Explanation:

• sudo: Required for administrative tasks.
• bcachefs format: Prepares partitions with the bcachefs filesystem.
• --label=ssd.ssd1: Labels the SSD partition for easy identification.
• path/to/ssd/partition: Actual SSD partition path that acts as a cache.
• --label=hdd.hdd1: Labels the HDD partition.
• path/to/hdd/partition: HDD partition path used for storage.
• --replicas=1: Specifies the number of data copies to maintain.
• --foreground_target=ssd: Targets the SSD for foreground I/O operations.
• --promote_target=ssd: Opts to promote frequently accessed data to the SSD.
• --background_target=hdd: Uses HDD for background storage tasks.

Example Output:

Formatting devices as RAID 0...
SSD /dev/sda labeled as ssd1, HDD /dev/sdb labeled as hdd1
RAID 0 configuration successful with SSD cache.

Use case 4: Mount a multidevice filesystem

Code:

sudo bcachefs mount path/to/partition1:path/to/partition2 path/to/mountpoint

Motivation: Mounting a multidevice filesystem enables the use of combined storage benefits from different partitions across more than one device. This option is advantageous when dealing with larger amounts of data spread across multiple drives for increased redundancy and performance.

Explanation:

• sudo: Permits the execution of the command with elevated privileges.
• bcachefs mount: This subcommand attaches numerous partitions as a single filesystem.
• path/to/partition1:path/to/partition2: Represents multiple partitions involved in forming one logical storage unit.
• path/to/mountpoint: Targeted directory location where the multidevice filesystem will be mounted.

Example Output:

Mounting devices /dev/sdx:/dev/sdy to /mnt/multisystem
Multidevice filesystem mounted successfully.

Use case 5: Display disk usage

Code:

bcachefs fs usage --human-readable path/to/mountpoint

Motivation: Understanding how disk space is allocated and used is crucial for effective storage management. Displaying disk usage in a human-readable format aids in comprehending space distribution quickly, allowing users to make informed decisions about managing available storage.

Explanation:

• bcachefs fs usage: Subcommand to check filesystem usage statistics.
• --human-readable: Converts the output into an easily understandable format with unit suffixes (KB, MB, GB).
• path/to/mountpoint: Specifies the filesystem for which to display usage data.

Example Output:

Filesystem /mnt/mybcachefs: Total: 500GB, Used: 250GB, Free: 250GB
Optimal space allocation ensured.

Use case 6: Set replicas after formatting and mounting

Code:

sudo bcachefs set-fs-option --metadata_replicas=2 --data_replicas=2 path/to/partition

Motivation: Increasing the number of replicas for metadata and data enhances resilience to disk failures. Post-formatting adjustments allow for tailored redundancy settings, ensuring critical data remains intact and accessible even in the event of hardware issues.

Explanation:

• sudo: Elevates permission needed for filesystem configuration changes.
• bcachefs set-fs-option: Alters filesystem settings post-creation.
• --metadata_replicas=2: Sets the number of metadata copies stored.
• --data_replicas=2: Sets the number of complete data copies.
• path/to/partition: Refers to the partition where these options are applied.

Example Output:

Replica settings updated: Metadata replicas = 2, Data replicas = 2
Redundancy enhanced successfully.

Use case 7: Force bcachefs to ensure all files are replicated

Code:

sudo bcachefs data rereplicate path/to/mountpoint

Motivation: The inability for data replication during initial operations or changes in hardware may necessitate enforcing data replication. Ensuring all files are duplicated provides insurance against data loss by bolstering redundancy capabilities through the entire filesystem.

Explanation:

• sudo: Ensures permission to enforce higher-level data activities.
• bcachefs data rereplicate: Forces the replication process to duplicate unreplicated data.
• path/to/mountpoint: Directory location pointing to where the mounted data resides.

Example Output:

Replicating data files in /mnt/mybcachefs...
All files successfully replicated across devices.

Use case 8: Display help

Code:

bcachefs

Motivation: Accessing help and documentation is crucial for understanding the full capabilities and nuances of the bcachefs command. Displaying the help section provides users with an overview of options they may not be familiar with and guidelines on how to implement bcachefs efficiently in their setup.

Explanation:

• bcachefs: Invoking the command without subcommands defaults to showing the help section that includes general usage, options, and subcommands.

Example Output:

Usage: bcachefs <command> [options]
Commands:
    format - Initialize a new bcachefs filesystem
    mount - Mount a bcachefs filesystem
    // Other commands...
Documentation available online at https://bcachefs-docs.readthedocs.io

Conclusion:

Utilizing the bcachefs commandline utility enriches system storage configurations by integrating high-performance caching mechanisms with robust data integrity and redundancy options. Whether formatting a new partition, mounting filesystems, or ensuring optimal data replication, bcachefs provides versatile tools for modern filesystem management, blending speed with reliability efficiently across various use cases.