1. A method in a computer system for retrieving data from one of multiple copies of the data, the method comprising: receiving a request identifying at least one data object to be accessed; querying an index to locate data copies that contain the identified at least one data object, wherein the data copies are created from similar source data, and wherein for each data copy the index contains an indication of the availability of the copy relative to other copies; determining one of the located data copies to use to access the identified at least one data object, wherein the determination is made based at least in part on the indicated availability contained in the index for each of the located data copies; and accessing the identified at least one data object using the determined one of the located data copies.