The Western Digital WD40EFPX is a 4 TB internal hard drive from the WD Red Plus series, specifically engineered for the demanding environment of Network Attached Storage (NAS). It is designed to provide a reliable way to store, protect, and share data for home offices, power users, and small to medium businesses, supporting RAID-optimized systems with up to 8 bays. This 3.5-inch drive utilizes CMR (Conventional Magnetic Recording) technology and a 256 MB cache to maintain steady performance, reaching a maximum sustained data transfer rate of 180 MB/s. Operating at 5400 RPM, it balances speed with power efficiency and quiet operation. To ensure stability in multi-drive setups, it features Rotation Vibration (RV) sensors and dual-plane balance control, which proactively counteract disturbances that could otherwise degrade performance over time. Built for continuous 24/7 operation, the drive is rated for a workload of 180 TB per year and boasts a mean time between failures (MTBF) of 1 million hours. It connects via a SATA 3 interface and weighs 570 g, fitting into a compact frame of 146.9 x 101.6 x 26.1 mm. With integrated NASware technology, the drive's parameters are fine-tuned to match NAS workloads, making it a dependable choice for those needing a stable, always-on data repository.