A method and system for determining priority is provided. The method includes generating a list defining specified data objects stored within a back-up/archived data storage system and applying importance levels to the specified data objects. Reliability urgency levels for the storage devices are determined and in response groups of data objects of the specified data objects are generated. Required reliability levels for each group of data objects are determined and associated erasure encoding rates are calculated. Fragment sets for the groups of data objects are generated and numbers of parity objects required for the fragment sets are determined. An erasure code algorithm is executed with respect to the groups of data objects and in response parity objects are computed on demand.