Here are detailed user stories for your Python module that manages directory audits on a Linux system:

### User Story 1: **Audit Directory Size**

**Title**: As a system administrator, I want to audit the size of directories to monitor data usage.

**Description**: 
The system should allow the administrator to initiate an audit of directories to calculate and store their current size. This audit will involve recursively traversing each directory and summing the size of all files within, including subdirectories. The results will be stored and used for comparison in future audits.

**Acceptance Criteria**:
- The system must be able to calculate the total size of a directory.
- The audit should include all files and subdirectories within the target directory.
- The audit results must be stored persistently for future reference.
- The system should handle directories containing large amounts of data (up to 100TB) efficiently.

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### User Story 2: **Track Directory Modification Times**

**Title**: As a system administrator, I want to track the last modification times of directories and their contents to avoid redundant audits.

**Description**:
The system should monitor directories for any changes, including the addition, deletion, or modification of files and subdirectories. Each directory's last modification time should be stored and checked before initiating an audit. If a directory and all its contents have not been modified since the last audit, the system should skip auditing that directory.

**Acceptance Criteria**:
- The system must record the last modification time of each directory and its contents.
- The system must compare the last modification time with the time of the last audit.
- If no changes have been detected since the last audit, the directory should be skipped in the current audit process.
- The system must accurately detect changes in large and deeply nested directory structures.

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### User Story 3: **Automated Auditing Process**

**Title**: As a system administrator, I want the system to automatically audit directories at regular intervals while skipping unmodified directories.

**Description**:
The system should support an automated auditing process that runs at configurable intervals (e.g., daily, weekly, monthly). During each audit, the system will check the modification times of directories and only audit those that have changed since the last audit. The process should be efficient and capable of handling the large data volumes typical in the environment.

**Acceptance Criteria**:
- The system must support configuring the frequency of automated audits.
- During automated audits, the system should skip directories that have not been modified since the last audit.
- The system must generate logs or reports detailing the results of each audit, including directories that were skipped.
- The system should handle errors gracefully and retry audits if necessary.

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### User Story 4: **Manual Audit Override**

**Title**: As a system administrator, I want to manually trigger an audit of a directory, even if it has not been modified, to ensure data integrity.

**Description**:
The system should allow the administrator to manually trigger an audit of any directory, regardless of whether it has been modified since the last audit. This feature is important for cases where data integrity needs to be verified or when changes are suspected but not detected by the system.

**Acceptance Criteria**:
- The system must provide a command or function to manually initiate an audit on a specified directory.
- The manual audit should override any checks on the last modification time.
- The results of the manual audit must be recorded and logged.
- The system should confirm the completion of the manual audit and display or store the results for review.

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### User Story 5: **Audit History and Reporting**

**Title**: As a system administrator, I want to review the history of audits and generate reports to track data growth and usage over time.

**Description**:
The system should maintain a history of all audits performed, including the size of each directory at the time of audit and whether the audit was automated or manual. The administrator should be able to generate reports based on this history to analyze data growth trends, storage usage, and audit frequency.

**Acceptance Criteria**:
- The system must store audit history data, including directory size, modification status, and timestamps.
- The system must allow the generation of reports summarizing audit history over specific periods.
- Reports should include insights on data growth trends, storage utilization, and directories audited most frequently.
- The system should provide an option to export audit history and reports in common formats (e.g., CSV, JSON).

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### User Story 6: **Efficient Handling of Large Data Volumes**

**Title**: As a system administrator, I want the system to handle large volumes of data (up to 100TB) efficiently to avoid performance bottlenecks.

**Description**:
Given the potentially massive size of the directories being audited, the system must be optimized to handle large data volumes without significant performance degradation. This includes optimizing file I/O operations, minimizing memory usage, and leveraging multithreading or other techniques to speed up the auditing process.

**Acceptance Criteria**:
- The system must efficiently traverse and audit directories containing large amounts of data.
- The system should use optimized algorithms to minimize the time required for auditing large directories.
- The system must provide feedback or progress indicators during lengthy audits.
- The system should be capable of running audits in parallel or using other performance-enhancing techniques to handle large datasets.

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These user stories should provide a comprehensive guide for developing your Python module for auditing directories on a Linux system. Each story addresses a critical aspect of the functionality, ensuring that the module is efficient, reliable, and user-friendly.