WD 4TB Red Pro 7200 rpm SATA III 3.5" Internal NAS HDD Engineered to deliver high performance and reliability to commercial and enterprise NAS environments, the 4TB Red Pro 7200 rpm SATA III 3.5" Internal NAS HDD from WD is well-suited for multimedia and creative pros, medium to large businesses, and commercial and enterprise NAS systems. Able to work in RAID-optimized NAS systems with an unlimited number of drive bays, this 4TB drive operates using a SATA III 6 Gb/s interface, a 256MB cache, and a rotational speed of 7200 rpm, which all help to ensure uninterrupted data transfers with a rate of up to 267 MB/s. This drive also features high levels of reliability, with 600,000 load/unload cycles, < 1 in 1015 non-recoverable read errors per bits read, a workload rate of 550TB per year, dual-plane balance control technology, and 2 million hours MTBF. Shock protection is provided by a multi-axis shock sensor and WD's NASware helps increase system compatibility, allowing Red Pro drives to be more easily integrated with your existing network infrastructure.