I'm glad I was able to help.
Yes, you should be able to map your DNS-321 to your MAC so the drive is available following boot. I know how to do this on a PC, but am not too familiar with the MAC OS. From what little I know you have to do the following:
- Go -> Connect to Server
- For the server address, enter: smb://[put_your_ip_address_here]/Volume_1
If this doesn't work or your need additional help, search on Google for mapping a networked drive on a MAC.