A company has acquired another company and is consolidating data centers. During the consolidation， half of the users of a business-critical application lost access. The users who maintained access experienced slow performance. What is the first action the SAN/storage administrator should take to determine the source of the problem（）

A. review SAN configuration， connectivity， and zoning
B. review application parameters for contention or tuning problems
C. use internal disk monitoring tools to determine the problem source
D. check the disk parameters in the OS setup on the system