A method of performing a migration of a physical extent in a redundant array of independent disks (RAID) storage system with a protection pool of storage units includes identifying a first physical extent of a first physical disk to be migrated to a second physical disk, wherein the first physical extent is associated with an array of physical extents distributed across physical disks of a storage cluster. The method further includes assigning a second physical extent from the second physical disk to the array to replace the first physical extent and migrating data from the first physical extent of the first physical disk to the second physical extent of the second physical disk.