1. A method for increasing data storage reliability in a heterogeneous storage system, the system comprising two or more storage devices of two or more different types, the devices storing respective data subsets of a dataset, the method comprising: accessing, via one or more processors, configuration parameters for the dataset stored on the storage devices, the configuration parameters including first and second amounts, U i and U 2 , respectively, of the data subsets respectively stored on the two or more storage devices; estimating, via one or more processors, an initial global reliability of the heterogeneous storage system for the dataset, based on the accessed configuration parameters; determining, via one or more processors, an increased global reliability of the heterogeneous storage system for the dataset, by estimating a global reliability as would be obtained by modifying at least some of the configuration parameters, whereby at least the first and second amounts of the data subsets respectively stored on the two or more storage devices are modified; and reconfiguring the dataset stored across the heterogeneous storage system according to the modified configuration parameters.