The Western Digital WD Red Pro WD221KFGX is a high-capacity 3.5-inch hard drive designed specifically for the demanding environments of RAID-optimized NAS systems. With a massive 16 TB of storage, it utilizes Conventional Magnetic Recording (CMR) technology to ensure consistent performance and reliability when handling large volumes of data across unlimited bay counts. The drive operates at 7200 RPM and features a 512 MB cache, allowing it to reach maximum transfer rates of 265 MB/s, which helps you move files quickly between networked devices via its SATA-3 (6 Gb/s) interface. To maintain stability in multi-drive setups, it incorporates Rotational Vibration (RV) safeguards and Time-Limited Error Recovery (TLER) to prevent system drops and keep your data accessible. The integration of NASware, OptiNAND, and ArmorCache technologies further optimizes its efficiency, supporting a heavy workload rating of 550 TB per year. This makes it a dependable choice for professionals or home lab enthusiasts running Windows, Linux, or macOS who need a drive capable of enduring a 2.5 million hour MTBF. Physically, the unit weighs 670 g and measures 147mm by 101.6mm, fitting standard server chassis. It is built to operate in temperatures ranging from 0°C to 65°C, ensuring it stays cool and functional during continuous 24/7 operation. Whether you are managing a large media library or critical business backups, this drive provides the scale and durability required for permanent network storage.