Those anxiously awaiting new top-end disk drives from IBM will be more concerned at the announcement of the final features of the 3990 Model 3 Storage Control Extended Functions, which will be made available in two steps. The Fast Write feature, which extends the benefits of cache performance to writing data, as well as reading data will be available in December as a microcode-only engineering change. Dual Copy, which provides a degree of fault-tolerance for cached volumes by maintaining two copies, will be available sometime in the first quarter of 1990. Dual copy device pairs are limited to like disk models, but 3380 Models A, D, and J can be paired with one another in any combination, but must have identical track and cylinder formats and identical capacities. Software support is provided in MVS/ESA and XA under MVS/DFP 3.1.0. The Extended Functions microcode releases take about an hour to install, and need a 3990 Initial Microcode Program Load.
