The Synology DX517 Expansion provides additional storage space for your Synology DS1517(+) or the Synology DS1817(+) NAS. Install up to 5 internal hard drives with a maximum storage capacity of 50TB. If you connect this expansion to your NAS, the device works immediately without you having to format the disks in your NAS. Manage them in RAID setups thanks to the Synology DSM software. Connect the device via the included eSATA cable. Does your NAS switch to energy-efficient standby mode? The DX517 also conforms to this mode to save power, and reduce the burden on your internal hard drives.