DOWNHOLE TOOL WITH PLURAL DATA STORES

A data logger comprising a first data store, a second data store and a controller connected to receive output from a temperature sensor indicating a temperature of the first data store. The controller may be configured to write data to the first data store and to switch to writing the data on the second data store if the indicated temperature of the first data store exceeds a first threshold temperature. The first and second data stores may be of different types. Upon the temperature of the first data store transitioning from above the first threshold to below the first threshold, the controller may be configured to copy any data recorded in the second data store to the first data store.