The sp_sysmon output for each data cache includes information that can help you determine the effectiveness for large I/Os in the Performance and Tuning: Monitoring and Analyzing for Performance book:
“Large I/O usage” on page 85 reports the number of large I/Os performed and denied and provides summary statistics.
“Large I/O detail” on page 95 reports the total number of pages that were read into the cache by a large I/O and the number of pages that were actually accessed while they were in the cache.
