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

The duperemove command is a utility designed to optimize your file system by identifying and optionally deduplicating duplicate filesystem extents. An extent is a small part of a file in the filesystem; on specific filesystems such as Btrfs and XFS, one extent can be referenced multiple times when portions of the files’ contents are identical. By finding and merging these duplicate extents, duperemove can help save disk space and improve storage efficiency. It is a particularly useful tool for administrators and users managing large quantities of data.

Use case 1: Search for duplicate extents in a directory and show them

Code:

duperemove -r path/to/directory

Motivation:

The primary motivation for searching for duplicate extents without immediately deduplicating them is to first assess how much redundancy exists within a filesystem. This step allows users to understand the potential for reclaiming disk space before applying more intrusive operations. By knowing the extent of duplication, users can make informed decisions about whether to proceed with deduplication and identify which directories or files may benefit the most from this process.

Explanation:

• duperemove: The command used to find duplicate extents.
• -r: This option tells duperemove to recursively search through the specified directory, including all subdirectories, ensuring a comprehensive scan.
• path/to/directory: This is the path to the directory you want to analyze for duplicate extents.

Example output:

Scanning: 100%
Comparing completed: processed 500 regular extents in file system
Found 100 duplicated extents in filesystem

Use case 2: Deduplicate duplicate extents on a Btrfs or XFS (experimental) filesystem

Code:

duperemove -r -d path/to/directory

Motivation:

Once duplicate extents have been identified, deduplication merges them to conserve disk space and improve storage efficiency. This use case is vital for users who have more extensive file servers or workstations where data redundancy may lead to increased storage costs or impact performance. Deduplication is particularly beneficial for filesystems with a lot of similar or repetitive data, such as backup directories or virtual machine image repositories.

Explanation:

• duperemove: The core command to execute deduplication processes.
• -r: Specifies that the command should search recursively through directories.
• -d: This flag enables the actual deduplication of detected duplicate extents, as opposed to merely identifying them.
• path/to/directory: The directory that you wish to deduplicate.

Example output:

Deduplication completed: deduplicated 100 extents in filesystem
Reclaimed 1024 MB of space

Use case 3: Use a hash file to store extent hashes (less memory usage and can be reused on subsequent runs)

Code:

duperemove -r -d --hashfile=path/to/hashfile path/to/directory

Motivation:

By utilizing a hash file, users can significantly reduce the memory footprint of deduplication operations and improve efficiency through data reuse. This use case is particularly beneficial for environments with limited resources or when the deduplication process needs to be run repeatedly, such as in routine maintenance tasks. The hash file stores calculated extent hashes, speeding up subsequent runs within the same directory structure by avoiding repeated calculations.

Explanation:

• duperemove: The command that initiates the hashing and deduplication processes.
• -r: Instructs duperemove to perform a recursive search.
• -d: Enables deduplication.
• --hashfile=path/to/hashfile: This option specifies a file where extent hashes are stored, reducing the need to recalculate them in subsequent runs.
• path/to/directory: The target directory for deduplication.

Example output:

Using hashfile: path/to/hashfile
Calculated 500 extent hashes
Deduplication completed using existing hashes
Reclaimed 512 MB of space

Use case 4: Limit I/O threads (for hashing and dedupe stage) and CPU threads (for duplicate extent finding stage)

Code:

duperemove -r -d --hashfile=path/to/hashfile --io-threads=N --cpu-threads=N path/to/directory

Motivation:

This use case is particularly useful for optimizing duperemove’s operations in terms of resource management, especially on systems where other processes demand substantial computational power and I/O bandwidth. By limiting the number of threads utilized, users can ensure that deduplication does not interfere significantly with system performance, allowing for a balance between efficiency and system responsiveness.

Explanation:

• duperemove: The command for extent identification and deduplication.
• -r: Conducts a recursive search.
• -d: Activates deduplication.
• --hashfile=path/to/hashfile: Specifies where to store extent hashes for reuse.
• --io-threads=N: Limits the number of I/O threads, where N is a user-defined number, during the hashing and deduplication stages.
• --cpu-threads=N: Restricts the number of CPU threads during the extent finding stage, setting an upper bound defined by the user.
• path/to/directory: Specifies the directory subjected to these operations.

Example output:

Using 2 I/O threads and 4 CPU threads
Using hashfile: path/to/hashfile
Deduplication completed with limited resources
Reclaimed 2048 MB of space

Conclusion:

The duperemove command is a powerful utility for managing disk space by identifying and deduplicating duplicate extents on filesystems. By understanding and applying these use cases, users can effectively optimize storage, achieve significant space savings, and maintain system performance. Each use case provides valuable insights into how duperemove can be tailored to meet specific needs, from basic extent identification to efficient resource management.