1. A computer program product comprising a non-transitory computer useable medium having a computer readable program, wherein the computer readable program when executed on a computer causes the computer to: measure system factors for a plurality of clusters over a plurality of instances, wherein the clusters are in communication over a network and each cluster comprises at least one tape volume cache; apply a smoothing function to the system factors, wherein recent instances have higher weights; calculate a mount-to-dismount lifespan for each cluster from the smoothed system factors; and select a source cluster for accessing an instance of a specified volume in response to the mount-to-dismount lifespans and a user policy.