Expansion Unit DX517 Effortless capacity expansion for Synology DiskStation solutions on-the-fly. 5-bay 3.5"/2.5" SATA expansion Easily add 5 additional drive bays to Synology DiskStation. Supporting both 2.5" and 3.5" SATA drives, DX517 is a flexible solution supporting on-the-fly volume expansion or serving as a local backup destination. Online volume expansion Managed from DiskStation Manager on the host NAS, the additional bays in the DX517 are immediately ready to be used once connected. On-the-fly volume expansion ensures that storage and services on the host are not interrupted during volume expansion. Hot-swappable drive tray design The hot-swappable drive trays of DX517 allow easy drive installation and replacement without powering down the system. Screwless drive tray design reduces the time needed for system setup. Dedicated local backup solution Synology DX517 can be used as a dedicated local backup solution for the Synology DiskStation. When created as a separate volume, the DX517 provides a great backup solution to its local hard disks in case of system failure