Three years later, Webster, a senior analyst and partner at Data Mobility Group LLC in Nashua, N.H., says, "Things haven't really changed all that much."

So what is it about heterogeneous SANs that inspires such long-standing fear, uncertainty and doubt?

No SAN is a homogeneous island

First, all SANs are multivendor by definition. No one vendor supplies all the networking components, switches, arrays, host bus adapters (HBA) and tape drives required to comprise a SAN. Most SAN configurations are usually sourced from a single vendor such as EMC Corp., Hitachi Data Systems Inc., IBM or Hewlett-Packard Co., each of which typically has a list of prequalified vendors with whom they work.

According to Tom Clark, director of solutions and technologies at McData Corp., agreements among these vendor partners commonly specify certain products down to the microcode level. Because of this granular, coordinated approach, vendors can protect themselves against users who deviate from interoperability dictates. If, for example, a user is attaching HBAs, the supplying vendor can suggest a preapproved list of vendors and that the user use certain specified levels of microcode. Despite its vendor focus, this arrangement is also favorable to users because when they comply, their service calls go a lot smoother.