I would suggest going out to s place like brentozar.com and getting the sp_AskBrent stored proc and running it to see what it tells you in terms of performance issues. another thing would be to look at Wait stats on SQL Server. go to sqlskills.com and search the site for Wait stats. You could create a sql agent job to run a rtace for queries that have a duration of over 100 milliseconds. You could look at sys.dm_io_virual_file_stats and see what the read/write latency is like. As you can see, there are a number of ways to approach a broad problem like this.