Keys of an index are associated with corresponding data chunks in a storage system. In response to a request for a particular key, a particular location is accessed in a first data structure which is maintained in a first storage using a first portion of the particular key. In response to the particular location containing a first value, indicating that the particular key is not present in the index. In response to the particular location containing a second value, a map is accessed using a second portion of the particular key to retrieve an entry in a second data structure maintained in a second storage. The second data structure provides a collision chain to link entries of the second data structure that share a common value of the second portion of the particular key. The first data structure, map, and second data structure are part of the index.