Synology DX510 DAS Hard Drive Array - 5 x HDD Installed - 15 TB Installed HDD Capacity - Serial ATA/300 Controller - RAID Supported - 5 x Total Bays - eSATA. Expansion Unit for Increasing Capacity of the Synology DiskStation Synology DX510 delivers an effortless solution for volume expansion and data backup for selected Synology DiskStations. The DX510 smoothly scales the storage capacity of the Synology DiskStation by an additional 5 hard drives on the fly when firmly connected directly to the Synology DiskStation, ensuring a reliable expansion solution.