There are a couple of simple ways to tell if your SAN performance needs tuning:

1.) If the application is not meeting response times, SLA's (Service Level Agreements), or customer service commitments.

2.) By using performance measurement software (IOstat, SAR, Perfmon etc), to drill down to discover specific I/O performance metrics. The most common symptom is disk I/O queuing where the queue depth is greater than 1. The greater the queue depth, the more significant the performance bottleneck.

There are of course other bottlenecks that exist in a SAN, of which many are server related, such as CPU and Memory as well as application-specific issues. A comprehensive performance review or audit can detect these types of bottlenecks and others.