The IBM XIV Storage System is designed to be cost-efficient in all aspects, while deliveringoutstanding and consistent performance. Which of these features is currently UNAVAILABLE onthe XIV system?（）

A.single-tier architecture supports all kinds of storage in one environment and makes scaling easy 
B.built-in thin-provisioning allows the acquisition and installation of additional capacity to bedelayed until needed. 
C.innovative use of solid state disk drives offers excellent capacity-for-cost value while meetingenterprise performance standards 
D.use of off-the-shelf components makes customized hardware unnecessary and makes itpossible to integrate state-of-the-art hardware assoon as it becomes available.