Client data is structured as a set of data blocks. A first subset of data blocks is stored on a current segment of the disks. A second subset of data blocks is stored on a previous segment. A request to clean client data is received, including a request to update the current segment to include the second subset of data blocks. The second subset of data blocks is accessed and transmitted from a lower layer to a higher system layer. Parity data is generated at the higher layer. The parity data is transmitted to the lower layer. The lower layer updates second mapping data. In the updated mapping of the second mapping data, each local address that references a data block of the second subset of data blocks is included in the current segment of the plurality of disks. The lower layer writes the parity data in the current segment.