Key Features. Plug & play online expansion USB cable safety bracket a secure connection Smart power sync helps to save power Smart temperature control for stable operation Supports My Archive cold backup technology Compatible with high capacity 18TB hard disks The AS6004U utilizes a USB (Universal Serial Bus) 3.0 connection cable. Simply plug it into any ASUSTOR NAS to complete hardware expansion! Depending on the model* ASUSTOR NAS devices can simultaneously connect up to 3 AS6004U units satisfying the high capacity storage demands of enterprise users. The AS6004U has a power sync mechanism that syncs it with the NAS's operation status. When the NAS enters sleep mode or powers off the AS6004U will enter into standby mode. When the NAS resumes normal operation the AS6004U will resume mounting. This function works to help users save significant power. The AS6004U features 4 hot swappable disk bays & is compatible with largest hard disks on the market. It supports RAID* & AES 256-bit encryption providing optimal data protection mechanisms..