If the troubleshooting algorithm determines that the issue is likely in the SAN Storage environment, and if the SAN Storage is provided by an element that the Foglight for Storage Management system is monitoring, the Analyze SAN Storage button appears in the Diagnosis panel.
The exact logic is somewhat complex. Basically, if the analysis points to a "possible" problem with SAN storage, AND the SAN storage is something monitored by FSM, then the button is shown. If there is no problem with storage detected, then the button is not shown. So if the graph on "Latency on Disk Extents..." is showing as all green, it means that there are likely no storage problems. That is the primary indicator used to determine when to show the button.
For more information, please refer here.