Hitachi HGST Ultrastar C10K900 HUC109090CSS600 - Hard drive - 900 GB - internal - 2.5" SFF - SAS 6Gb/s - 10000 rpm - buffer: 64 MB Ultrastar C10K900 is a 2.5-inch 10,000 RPM hard drive that leads the industry with 18% faster sequential and up to 17% random performance than the nearest competitor. The high-performance SAS 6Gb/s interface delivers data reliability, availability and scalability and is the only small form factor SAS drive in the industry to pack a 64MB cache buffer for optimized read/write response time.