Mechanisms for performing a backend operation in a file system are provided. A backend operation on a portion of the file system is initiated. At least one indirect transition table data structure is created for performing the backend operation. Metadata corresponding to the portion of the file system is linked to the at least one indirect transition table data structure. The backend operation is performed on data in a sub-portion of the portion of the file system and the at least one indirect transition table data structure is updated with pointers to new locations of the data in the sub-portion as transitions of the data are completed. At least one data access operation is performed to the portion of the file system at substantially a same time as performing the backend operation on the data in the sub-portion of the portion of the file system.