1. A method of predicting response time for a storage request comprising the steps of: a computing entity: storing a training data set comprising past performance observations for past storage requests of a storage array, each past performance observation comprising an observed response time and a feature vector for a particular past storage request, the feature vector comprising characteristics that are available external to the storage array, and the feature vector including a locality feature that relates the particular past storage request to one or more earlier storage requests; forming a response time forecaster from the training data set, which includes applying a probability model to the training data set, where the probability model models a likelihood of a cache hit dependent upon the locality feature; and applying the response time forecaster to a pending feature vector for a pending storage request to obtain a predicted response time for the pending storage request, wherein the predicted response time is based on the likelihood of a cache hit.