1. A computer-implemented method comprising: receiving requests to store a plurality of data objects in a storage system, the storage system having a primary storage and a secondary storage that are different types of storage; adding a data object to one of a plurality of files in the secondary storage, the file storing the plurality of data objects, each data object having a first set of metadata that is stored with the data object in a data container in one of the plurality of files; generating index data including a second set of metadata for each data object, the second set of metadata representing an offset location for each data object and a size of each data object in the file in the secondary storage; and storing the index data including the second set of metadata in the primary storage for locating data objects in the file in the secondary storage.