Patent ID: 8051259

Claim:
A computer implemented method for storage de-allocation during a clean process, the computer implemented method comprising: determining whether to perform the clean process for a target disk of a plurality of disks in a storage system; responsive to a determination to perform the clean process, identifying a first grain in the target disk, an upstream map for the target disk, and a downstream map for the target disk; comparing an entry for the first grain in the upstream map with an entry for the first grain in the downstream map; determining whether the entry for the first grain in the upstream map is different than the entry for the first grain in the downstream map to identify whether a set of discrepant bits is present; responsive to determining that the entry for the first grain in the upstream map is different than the entry for the first grain in the downstream map, copying data from the first grain to a second grain in a second disk of the plurality of disks, wherein the second disk is downstream from the target disk; setting the entry in the downstream map to be the same as the entry in the upstream map; determining whether the first grain has been allocated to a space efficient storage unit; and responsive to determining that the data from the first grain has been allocated to the space efficient storage unit, de-allocating the first grain from the target disk.