No network is bulletproof. Even with careful selection of network equipment, cabling, and management applications, eventually something will break. The challenge then is to minimize the down time caused by a failure and keep the rest of the network operational. Because SANs represent the fusion of networking and storage, storage networks inherit both the strengths and the weaknesses of each. In addition, upper-layer applications may not always behave as advertised, further complicating diagnosis and isolation of problems. This chapter examines some of the basic problem-isolation techniques used in SAN environments and the tools available to monitor the health of the storage network.