To properly document that certain data storage is necessary for system functionality during the AppExchange Security Review:
1. **Disclose Data Storage Locations and Providers**: Clearly identify where your solution stores or processes data, including the countries and providers (e.g., AWS, Azure, Google Cloud Platform).
2. **List Sensitive Data**: Provide a detailed list of all sensitive data your solution processes or stores, such as personally identifiable information, payment data, or health data.
3. **Explain Necessity**: Include an explanation of why the data storage is essential for the system's functionality.
This documentation ensures transparency and compliance with the security review requirements. Let me know if you need help drafting this!