I have heard that storing indexes on a different filegroup and drive increases performance in a database because the drive doesn't have to go back and forth between the index and the data to which the index refers. I have also heard that this is a myth.
When is it advisable to store nonclustered indexes on a separate filegroup and drive? What perfmon/profiler evidence would lead me to arrive at that conclusion? Does hardware play a role in the decision (whether a RAID/SAN is used over a single drive)?