Microsoft Azure Architect Design (AZ-301) Practice Exam

What caching policy provides the best performance for a data disk used to store log files in a SQL Server virtual machine?

1. None

2. Read Only

3. Read/Write

4. No caching needed

The correct answer is: None

When considering caching policies for a data disk that stores log files in a SQL Server virtual machine, the best performance is achieved by selecting a caching policy that aligns with the nature of log file operations. In this case, using "None" for the caching policy is advantageous because it ensures that all I/O operations are directly sent to the underlying disk without any intermediate caching layer. Log files are critical for SQL Server operations, particularly for maintaining ACID properties (Atomicity, Consistency, Isolation, Durability), which require that changes be written to disk as soon as they occur. By not caching the log file data, the system can avoid potential delays or inconsistencies that might arise from cached writes. This ability to perform direct writes ensures that the data integrity is maintained and that the performance is optimized, especially in scenarios with high I/O transaction rates commonly associated with log file usage. Choosing any other caching policy, such as "Read Only" or "Read/Write," could introduce latency in write operations because the system would first update the cache before writing to the disk, which is not ideal for log files that need immediate durability. The option that states "No caching needed" might suggest a lack of optimization, but it's more about not applying caching mechanisms that