Abstract: The invention provides system, apparatus, method, and computer program for dynamically expanding a storage system, particularly a RAID (Redundant Array of Independent Disks) set based storage system, while assuring data integrity during the expansion process. In one embodiment, the invention provides a method for redistributing data in a data storage system. This embodiment of the method includes the steps of: identify data in a destructive zone of the storage system; migrating data before reaching the destructive zone from source storage devices to destination storage devices; copying data onto a number of backup buffers; mirroring data backed up in the copying step onto free space in the storage system; migrating data backed up in the mirroring step to destination storage devices; repeating the steps of migrating, copying, and mirroring, until data that will be in the destructive zone is migrated out of the destructive zone; and migrating remaining data from the source disks onto the destination disk.