Traditional storage arrays permit the configuration of multiple disk types within a single array. This can range from solid state disks (SSDs), through to fast fibre channel drives and slower high capacity SATA drives. USS operates a slightly different model – all drives in the USS array are high capacity SATA. SSD drives are then used to ameliorate performance on read and write activity in combination with the ZFS file system, by using the SSDs for read caching and write logging.