To add and set up an expansion unit, the knowledge base gives these steps for the RX1214 guide:
1. Install the drives in the expansion unit first.
- For 3.5" drives: place the drive in the tray, turn the tray upside down, and tighten the screws in the four spots.
- For 2.5" drives: do the same.
- Insert the loaded tray into the empty drive bay and make sure it is pushed in all the way.
- Push the handle inward to secure the tray.
- Repeat for the other drives.
- If you plan to create a RAID volume, Synology recommends that all installed drives be the same size to optimize capacity usage.
- Warning: if a drive already contains data, the system will format it and erase all data, so back it up first. [1]
2. Connect the expansion unit to the RackStation.
- Connect one end of the power cord(s) to the expansion unit and the other end to the power outlet(s).
- Connect one end of the expansion cable to the expansion unit, and the other to the NAS. The fragment cuts off after that point, so it does not show the full connection sentence. [1]
3. For expanding storage capacity in DSM, the knowledge base also says:
- Open Storage Manager.
- Go to Storage Pool.
- Select the pool you want to expand.
- Click Add Drive from the Action drop-down menu.
- Select the drives and finish the wizard. [9][10]
4. For expanding a volume, the storage pool/dual pool must be RAID 1, RAID 5, RAID 6, or RAID TP, the system must be healthy, and the available drive must match the existing drive type and be at least as large as the smallest drive in the volume. [13][14]
I don’t have a complete model-specific setup procedure for DX/RX units beyond what is in the RX1214 guide fragment. Also, one forum fragment notes that drives in a DX or RX may appear as removable eSATA drives if that DX/RX model is not supported by the NAS model. [11]
Sources used: [1], [9], [10], [11], [13], [14]