Western Digital Ultrastar DC HC550 18TB SAS 12 Gb/s 512MB 3.5" internal hard drive WUH721818AL5204

Enterprise capacity drive

The Western Digital Ultrastar DC HC550 delivers 18TB of storage on a SAS 12 Gb/s interface for server and data-centre workloads. It targets administrators who need high areal density on a 3.5-inch form factor with 512MB of cache to absorb bursty write traffic. The HelioSeal platform and CMR recording keep the drive in its lane for sequential-heavy object-store tiers.

18TB headroom and limits

Nine disks combine to reach 18TB, giving object storage and erasure-coded pools room to scale before another shelf is justified. The 2.5M MTBF rating and 600,000 load/unload cycles indicate design for always-on duty rather than occasional backups. Random small-block performance and latency-sensitive databases will exhaust IOPS long before capacity fills.

Helium-sealed build and SAS connectivity

HelioSeal hermetic sealing reduces turbulence and power draw across the nine-platter stack, while the SAS 12 Gb/s port enables dual-port multipath cabling in standard drive bays. Unlimited drive-bay support means the unit fits existing 3.5-inch hot-swap cages without special brackets. The 512e/4Kn sector format eases integration with modern storage controllers.