WD Red 4TB 3.5" NAS Hard Drive (WD40EFZX) - Capacity: 4 TB, Interface: SATA, Form Factor: 3.5 in, Cache Size: 256 MB, Disk Speed (RPM): 5400rpm, Compatibility: Designed with SMR technology for workloads associated with personal and home office, such as storing, archiving and sharing, in RAID-optimized NAS systems with up to 8 bays.