1. A method of destaging a write cache in a storage system having an array of storage disks, the array being ordered in an sequence of write groups, wherein the write cache is shared by the disks, the method comprising the steps of: a) placing ones of the write groups in the write cache temporarily, responsive to the ones of the write groups being written to the array; b) listing the write groups stored in the write cache in order of the sequence in the array, wherein the listing is circular, so that a lowest one of the write groups is listed next to a highest one of the write groups; c) selecting the listed write groups in rotation according to the sequence; and d) destaging such a listed write group from the write cache to the disk responsive to i) the selecting of the write group and ii) a state of a recency indicator for the write group, wherein the recency indicator shows recency of writing to the write group.