With 4 TB of storage, this is a good hard drive if you need a larger storage unit. This model's rotation speed is 5 400 rpm.
From Digitalpromo
WD 4TB 3.5inch SATA3 PURPLE Surveillance Hard Drive, Intellipower,...
AA2Z Supply
WESTERN DIGITAL WD40PURX WD PURPLE 4TB 5400RPM (INTELLIPOWER) SATA-6GBPS 64MB BUFFER 3.5INCH INTERNAL SURVEILLANCE HARD DISK DRIVE. BULK. .
Athema Services
western digital wd purple 4tb 24x7 wd40purx - eet01