An indication of one or more changes to file system data since a last backup snapshot is received. One or more changes to the file system data between a requested backup version and the last backup snapshot are determined based in part on differences between a first tree data structure corresponding to the requested backup version and a second tree data structure corresponding to the last backup snapshot. The differences correspond to the one or more changes to the file system data between the requested backup version and the last backup snapshot. One or more data blocks corresponding to the one or more changes to the file system data since the last backup snapshot and one or more data blocks corresponding to the one or more changes to file system data between the requested backup version and the last backup snapshot are provided to a primary system.