A computer-implemented method, computer program product and system for dynamic granularity of a data storage by identifying tiers of data including units of data with a unit heat index, corresponding to an activity level metric and identifying a tier heat index for each of the tiers of data corresponding to an average of the unit heat index for the units of data within the tiers of data. Furthermore determining a granularity index based on a size of the units of data; calculating a pairing index by comparing the unit heat indexes from the corresponding tiers of data and calculating an efficiency index by comparing the unit heat indexes indicating a percentage of the of units of data within a first tier of data with a higher unit heat index than all of the units of data within a another tier of data with a lower tier heat index.