The combination of large I/O and asynchronous prefetch can provide rapid query processing with low I/O overhead for queries performing table scans and for dbcc operations.
When large I/O prefetches all the pages on an allocation unit, the minimum number of I/Os for the entire allocation unit is:
31 16K I/Os
7 2K I/Os, for the pages that share an extent with the allocation page
Reference to Large I/Os are on a 2K logical page size server. If you have an 8K page size server, the basic unit for the I/O is 8K. If you have a 16K page size server, the basic unit for the I/O is 16K.