This disclosure provides a method, a computing system and a computer program product for managing storage capacity usage in a storage system. For each of a plurality of logical storage arrays in the storage system, a Remaining Time Buffer (RTB) measure indicating time to use up respective free space currently available to the logical storage array is calculated. Respective free space currently available to each of one or more of the plurality of logical storage arrays is adjusted, so that the RTB measures of the one or more logical storage arrays satisfy a threshold.