http://forum.synology.com/wiki/index.php/How_to_Manage_the_Synology_RAID_Volume Can the Synology RAID grow with additional storage?
Multi-bay Synology Disk Stations using Redundant RAID Volumes are capable of growing in storage capacity in the following ways
Vertically Where smaller disks are incrementally changed to larger disks, ie 2x500GB Disks in RAID-1 are replaced with 2x2TB Disks, in RAID-1 Horizontally Where additional disks are added to an existing RAID Volume, ie, 2x500GB Disks in RAID-1 is converted into 4x500GB Disks in RAID-5 Plug-and-Use Expand Applicable to the DS509+ with DX5 (or RS409+ with RX4), where the volume from the DS509+ is expanded onto the HDD Volume located on the DX5.