DAS vs. SAN performance is an interesting question and the answer is not straightforward as it depends on many factors. DAS perform much faster than SAN if it is configured and used properly (as you can have many dedicated spindles forming a local RAID6 or RAID10 volume and you can have these separate volumes spanning different spindles, which is ideal for RDBMS systems).

When using SAN, we don’t always get volumes spanning different spindles as they are shared among many servers. Also, using SANs entails longer and shared I/O paths when compared to a shorter and dedicated I/O path of a DAS and more chance that one of the components can become a bottleneck as the I/O path is shared among many servers. However, SAN is unbeatable in availability, scalability, maintenance, and reliability but performance is a different beast. A SAN administrator with a DBA background will probably configure SAN in a much more optimal way to help the performance of DB systems

To read more, please visit Satish Kartan's blog here www.sqlfood.com, where he has shared more details on this.