1. A method for increasing data storage reliability in a heterogeneous storage system, the system comprising two or more different types of storage devices, 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 respective amounts, comprising U 1 and U 2 , of the data subsets respectively stored on the two or more different types of 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 including the respective amounts of the data subsets stored on the two or more different types of storage devices; 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, wherein at least the respective amounts U 1 and U 2 of the data subsets stored on the two or more different types of storage devices are modified to increase the global reliability of the heterogeneous storage system for the dataset; and reconfiguring the dataset stored across the heterogeneous storage system according to the modified configuration parameters including the modified respective amounts of the data subsets stored on the two or more different types of storage devices.