Keep a compatible Buffalo storage system in service with a 4 TB replacement hard drive designed for DriveStation Ultra deployments. The OP-HD4.0BN/B is intended for direct replacement in the HD-DN040T/R6 platform, giving administrators a straightforward path to recover capacity after a drive issue without reworking the storage stack. For NAS environments, the replacement part has to do more than fit physically. It has to match the system’s expectations for interface, form factor, and deployment role. This drive is specified as an internal 3.5 in SATA model, which makes it a practical choice for maintaining the original storage architecture and reducing the risk of compatibility surprises. The value here is operational certainty. A purpose-matched replacement drive supports faster restoration, cleaner spare-part planning, and less time spent validating hardware during an outage window. With a 3-year limited warranty, it also gives procurement teams a clearer support horizon for long-lived storage infrastructure.