You are responsible for the reliability of a high-volume enterprise application. Users report that a critical data-intensive reporting feature consistently fails with HTTP 500 errors. Investigation reveals a strong correlation between failures and the size of an internal queue used for report generation, traced to a reporting backend with high I/O wait times. After resolving the issue by resizing the backend's persistent disk (PD), you need to define an availability Service Level Indicator (SLI) for the report generation feature. How would you define it?