How to Use the 'compsize' Command (with Examples)

The compsize command is a powerful tool used to calculate the compression ratio of files on a Btrfs filesystem. It allows you to analyze how much space is being saved by compressing files, providing valuable insights for managing disk usage efficiently. Ideal for both system administrators and power users, compsize uncovers the space-saving benefits that can be achieved with different compression methods on Btrfs systems. Below, we delve into specific use cases of the compsize command to illustrate its versatility and usefulness.

Use case 1: Calculate the Current Compression Ratio for a File or Directory

Code:

sudo compsize path/to/file_or_directory

Motivation:

Understanding the current compression ratio of a file or directory helps in assessing the efficiency of data storage. If you’re managing a server with limited disk space or optimizing a personal computer for better performance, knowing which files benefit most from compression can be crucial. It allows you to make informed decisions about data management and can guide future strategies for effectively using Btrfs compression.

Explanation:

• sudo: This command requires root privileges to access and analyze file metadata on the filesystem.
• compsize: The main command we are focusing on; it calculates compression ratios.
• path/to/file_or_directory: This specifies the target file or directory whose compression ratio we want to determine. Replace this portion with the actual path of your file or directory of interest.

Example output:

Type       Perc     Disk Usage   Uncompressed Referenced  
TOTAL       80%        4.0G          5.0G        5.0G

In this example, the output reveals that 20% of space is saved due to compression, with the total uncompressed data being 5.0G and the disk usage being 4.0G.

Use case 2: Don’t Traverse Filesystem Boundaries

Code:

sudo compsize --one-file-system path/to/file_or_directory

Motivation:

When dealing with servers or systems that host multiple filesystems, it becomes necessary to confine operations within a specific filesystem boundary. This prevents unintentional analysis of other mounted filesystems which may not be relevant to your current inquiry. Using this option ensures that the output pertains strictly to the specified filesystem, providing a precise and isolated analysis.

Explanation:

• sudo: Required to run compsize with the necessary permissions.
• compsize: The command used to calculate the compression.
• --one-file-system: This option tells compsize not to cross into other filesystems. It’s useful for ensuring that only the storage of the specified filesystem is analyzed.
• path/to/file_or_directory: As before, this indicates the target directory or file path for the examination.

Example output:

Type       Perc     Disk Usage   Uncompressed Referenced
TOTAL       75%        2.0G          2.67G       2.67G

The output reports a 25% space saving strictly within the chosen filesystem’s boundary, emphasizing the benefits of compression without overstepping into other potentially mounted filesystems.

Use case 3: Show Raw Byte Counts Instead of Human-Readable Sizes

Code:

sudo compsize --bytes path/to/file_or_directory

Motivation:

In contexts where exact byte counts are preferred over approximations (like in scripted, automated analysis tasks or when verbatim results for auditing purposes are necessary), displaying raw byte counts can be immensely valuable. Users can integrate this detailed output into databases or further processing scripts for enhanced granularity and precision.

Explanation:

• sudo: Ensures compsize runs with the correct permissions to access necessary file information.
• compsize: The core command used to check compression.
• --bytes: This option instructs compsize to display results in raw byte counts rather than in a rounded and human-readable form (like KB, MB, or GB).
• path/to/file_or_directory: Denotes the precise target location for compression evaluation, needing user-defined path input.

Example output:

Type         Disk Usage   Uncompressed Referenced
TOTAL        2147483648   2684354560   2684354560

This output shows the exact sizes in bytes, which can be critical for applications requiring precise storage metrics instead of using file size approximations.

Conclusion

The compsize command is an indispensable utility for gauging the effectiveness of Btrfs file compression. Whether you’re concerned with routine system management, space optimization, or precise data audits, its diverse features accommodate various technical needs. By using this tool effectively, users can capitalize on data storage efficiencies, better managing system resources and optimizing filesystem performance.