4TB IronWolf Pro 3.5 HDD SATA 6 Gb/s 7200 RPM Cache 128MB Up to 24 bay supported. IronWolf is purpose built for NAS and comes standard with a 3 year Limited Warranty and 180TB/yr workload rating, 1M hour MTBF. IronWolf Pro comes standard with a 5 year Limited Warranty and 550TB/yr workload rating, and 1.2M hour MTBF. IronWolf Pro comes standard with 2 years of Seagate Rescue data recovery service in case of physical damage, natural disaster, malicious attacks and more. SINGLE PACK