A mapped RAID system with a protection group of physical data storage drives calculates an affinity value for each pair of physical data storage drives in the protection group that is equal to a total number of RAID extents to which at least one drive extent is allocated from each of the physical data storage drives in the pair. A change from a previous level of RAID protection to a new level of RAID protection provided by one of the RAID extents is detected. The new level of RAID protection provided by the RAID extent uses fewer drive extents than the previous level of RAID protection provided by the RAID extent. The disclosed technology selects one of the drive extents previously allocated to the RAID extent for deallocation such that the range of the affinity values is minimized after deallocation of the drive extent.