WD Purple Surveillance Hard Drive 4TB WD42PURZ Features: Capacity up to 8TB Engineered specifically for mainstream surveillance systems AllFrame™ technology delivers optimizations for write-intensive, low bit-rate, high stream-count workloads typical to mainstream surveillance applications Supports up to 180 TB/yr workload rate Support for up to 16 bays Tarnish-resistant components 3-year limited warranty Specifications: Capacity 4 TB Interface SATA Form Factor 3.5 Inch Recording Technology CMR Interface transfer rate (max) Buffer to host 6 Gb/s Interface transfer rate (max) Host to/from drive (sustained) 175MB/s Cache (MB) 256 Annualized workload rating 180TB/yr MTBF 1,000,000