There are has been a lot of confusion about how to correctly wire a Dell C6220 3 Node Server to make a 4 Node Server and vice versa. 

This is an explanation of what we see most of the time with the 3 and 4 Node units we get.

With the Dell C6220 rack servers, whether it's a 3 or 4 nodes, each node supports 4 drives with a single mini-SAS to 4/3 SATA cable.

The daughter board on the right of the nodes (when looking at the system from the front) has two rows of mini-SAS ports. Only the "HDD 1-4" for each node seems to work with each node.

They are organized just like the nodes:

• The top left two mini-SAS ports are the top left node. 
• The top two right mini-SAS ports are the top right node. 
• The bottom left two mini-SAS ports are the bottom left node. 
• The bottom right two mini-SAS ports are the bottom right node.

The C6220s only have 12 HDDs total.

The 3 Node uses three mini-SAS to 4 SATA.
Each node is connected to each row. The third row back-plane doesn't get a SPDIF connector.

1. The top left is the top left node, which is connected to the top row of HDDs.
2. The bottom left is the bottom left node, which is connected to the middle row of HDDs.
3. The bottom right is the bottom right node, which is connected to the bottom row of HDDs.
4. 

The 4 Node uses four mini-SAS to 3 SATA.
Each node is connected to each column.

1. The top left is the top left node, connected to the left column of HDDs.
2. The bottom left is the bottom left node, which is connected to the second column of HDDs.
3. The top right is the top right node, which is connected to the third column of HDDs.
4. The bottom right is the bottom right node, which is connected to the far right column of HDDs.