Create a new volume on a Synology NAS after adding a DX517 expansion unit

Whether you're creating a new storage pool and volume on your main NAS or your expansion unit, it all starts with this support document.

https://kb.synology.com/en-us/DSM/hel...

Once physically connected, the fact that your new drives are in the storage unit is irrelevant in comparison to placing new drives in empty bays of an existing NAS.

The expansion unit is a literal extension of your NAS connected by a cable.

Near the end it took me a few minutes to realize that I had to go into control panel and then Shared Folder to create a test network share on the new volume, instead of flubbing around in File Station a few times before reality sunk in.