Design a Cloud Storage Gateway

Design a storage gateway appliance that presents a local file-system or block-device interface to on-premises applications while transparently tiering data to cloud object storage. Hot files are served from a local SSD cache with LRU eviction; cold files are fetched on-demand from the cloud. Support bandwidth throttling, encryption at rest and in transit, multi-site access with conflict resolution, and snapshot-based backups to cloud archives.