You’ve issued your select query – the data isn’t in memory and so you’ve got to go to disk to get it. There are no dwarves to help you so the question is - How is this satisfied? What exactly is read-ahead? Does the edition you have installed affect how this is performed? Does partitioning alter anything? That’s just the half of it – there’s writes to talk about too. Understand the fundamentals of SQL Server I/O in this one hour practical session.