According to Dell's official best practices for Unity XT hybrid arrays, the recommended minimum amount of Flash capacity for a hybrid pool is 10%. This recommendation ensures that the FAST VP (Fully Automated Storage Tiering for Virtual Pools) feature has a sufficiently large high-performance tier to store the most active data, or "hot" data. The Dell Sizer tool, including the System Designer option, is built upon these best practices to guide architects in creating balanced and performant configurations. Allocating at least 10% to the Flash tier provides a strong starting point for performance in most mixed-workload environments.

A. 5%: While 5% might be considered an absolute bare minimum in some older contexts, the current and official Dell best practice recommendation is higher to ensure better performance.

C. 15%: This percentage is greater than the recommended minimum. While adding more flash can improve performance, it is not the baseline recommendation for initial system design.

D. 7%: This is not a standard value cited in Dell's best practice documentation for Unity XT hybrid pool design.

1. Dell Unity: Best Practices Guide (H15163.8), Page 21, Section: "Hybrid pools". The document states, "For hybrid pools, it is a best practice to configure at least 10% of the pool capacity as Flash. This provides a large enough tier to accommodate frequently accessed data."

2. Dell Unity: Dynamic Pools White Paper (H15200.4), Page 10, Section: "Best Practices". The paper states, "As a best practice, Dell Technologies recommends configuring at least 10% of the pool capacity as Flash drives."

3. Dell Unity: FAST Technology Overview White Paper (H15084.5), Page 9, Section: "FAST VP Best Practices". The document notes, "As a general best practice, it is recommended to start with 5-10% of Flash capacity in a hybrid pool." The 10% figure represents the more robust and commonly cited recommendation for optimal design.