A fault-tolerant monitoring apparatus is arranged to monitor physical performance properties of a plurality of networked computing elements, each element including a processing unit and individual memory. The monitoring apparatus comprises a plurality of measurer apparatuses, each arranged to measure the physical performance properties of a single computing element, the physical performance properties being stored as local information in the individual memory of the computing element in which the measurement is made; and one or more collector apparatuses arranged to control collection of remote information representing physical performance properties from individual memory in a plurality of the computing elements; and storage of the remote physical performance information as replicate information in the individual memory of another computing element; wherein the remote physical performance information is collected using third party access.