Generally you can access the DDP Areca RAID card interface from the web GUI "RAID cards" page.
However when the GUI is not available, you can connect an ethernet cable from your client machine directly to the RAID card ethernet port as show below:
From there you should be able to ping the RAID card, the default IP address is 172.16.5.100 (subnet 255.255.0.0) for the first RAID card, 172.16.5.101 (subnet 255.255.0.0) for the second one, etc. So your client machine port should have an IP address and mask within the same subnet, like 172.16.5.20 (subnet 255.255.0.0) so that you can ping the RAID card.
You might need to change your hardware settings in the OSX network preferences panel in order to communicate properly to the RAID card, make sure the NIC is getting configured "automatically" as shown below:
If you still cannot ping your RAID card, the default IP addresses might have been changed, which you can check by rebooting the DDP and plugging a keyboard and monitor to it. During the boot sequence, you must hold the tab key when you see the following message:
You will then have to select the controller which you need to check the IP by selecting one the appearing entries.
When you have only one RAID card in your DDP, select the only one entry which appears as shown below:
A new menu will show up with a few entires, select "Ethernet Configuration" in order to see the current network settings.
If needed you can modify the RAID card IP address be pressing the enter key: