If you query for local SSDs during creation of a Flash Read Cache resource, the ESXi host might not return a complete list of the local SSDs.
ESXi might not be able to automatically detect SSDs, or recognize them as local.
ESXi does not recognize certain devices as SSDs when their vendors do not support automatic SSD detection. In other cases, some non-SATA SAS SSDs might not be detected as local. When disks are not recognized as local SSDs, they are excluded from the list of SSDs available for such features as Flash Read Cache because the feature requires only local SSDs.