How to choose rack and PDU for Cisco Nexus 7000

          Cisco Nexus 7000 has gain popularity in the past year. Given its size, there is always a question regarding the type of rack needed to house the switch especially for those who are the first-time installer. In this article, I will provide quick tips on how to choose a rack for a Cisco Nexus 7K, specifically for Nexus 7010 and 7018, as well as some ideas for PDU selection. Obviously, there are many manufacturers that you can choose from so the article will present in a vendor-neutral fashion.

Nexus 7010
           Below is the diagram from Cisco documentation. The depth of the chassis including the front cable management is 38 inches. Cisco recommends front-to-back racking space of 46 inches. So the options are the followings in order of preference.




          For 4-Post rack

          1. In my opinion, if there is no compelling reason to have the chassis in a cabinet, this is a preferred option for the reason being that the front and back are open. Although you should still ensure the front and back clearance, you have more flexibility and do not need to worry about the chassis not being to fit into a cabinet. Cisco requires the depth of at least 24 inch (610mm) for the mounting bracket. You will also be better off with a bottom horizontal PDU unless you can somehow manage to install vertical ones.
 
          For cabinet-style rack

          1. A rack with 47-inch (1200mm) or deeper and adjustable mounting rail, as you will need to move the front rail back a few inches to accommodate the cable management on the Nexus is a recommended cabinet option. You will have enough rear space for vertical PDUs (as permitted by the cabinet) and cabling. You should also be able to close both front and back doors.
          2. A rack with 42 to 47 inch (1070-1200mm) in depth and adjustable mounting rail will leave you minimal rear space for cabling, and most likely prohibit the use of vertical PDU. In this case, bottom horizontal PDUs would work best. You should still be able to close the door but this depends on space left in the rack.
          3. Any rack with less than 42 inch (1070mm) in depth will most likely not be able to accommodate the chassis unless you plan to leave the back of cabinet open and have cables hanging outside. I would advise against this option.
 

Nexus 7018
           Below is the diagram from Cisco documentation. You can see the physical chassis width and depth remain the same as 7010 so our previous discussion on the depth of the rack still applies. However, there is now a requirement for side clearances as the 7018 has side-to-side airflow. 



          For 4-Post rack

          1. Again, in my opinion, this is the prefer option. In addition to previous discussion, you will need to leave enough space of at least 11 inch (280mm) on each side especially if the adjacent rack is also a 7018. 

          For cabinet-style rack
          
          1. Unless you can get an extra wide rack to accommodate airflow, you will most likely need to remove the side panels and leave at least 11 inch (280mm) to adjacent racks,
 
Tips on PDU:
           In most cases, horizontal PDUs are the best option but vertical PDUs also work fine as long as there is extra room to securely mount them in the cabinet without interfering with the chassis. Some rack vendor design their rack to specifically accommodate their vertical PDUs. Each Nexus power supply has two power inputs so you may need up to six outlets (three power supplies) for 7010 or 8 outlets (four power supplies) for 7018. 
          For example, given power sources are two three-phase circuits, you can buy two three-phase PDUs with at least six C-19 outlets each and connect the power supplies to them such that if one circuit fails, all power supplies continue to function using the other circuit (ie. grid redundancy). This will result in 2:1 power share but should work fine in most cases.

Other Tips:
          - Some PDUs, three-phase in particular, have very thick power cord and large connector. They might have trouble getting through a hole, either top or bottom, to exit the cabinet. In which case, you will have trouble closing the back door.
          - For a 4-post rack, install vertical cable managements on both sides
          - Although you may think the majority of cables are at the front and there is no need for back space, the power cords at the back will need a few inches themselves so it is always wise to have some back space.

Check List:
          1. Choose proper racks per guide above
          2. Know the type of power source (ie. Single-Phase, Three-Phase)
          3. Ensure sufficient quantity of power source 
          4. Choose proper PDUs (ie. vertical VS horizontal, input/output power, quantity of outlets, type of connectors) and sufficient quantity of outlets
          5. Make sure the power cords ordered with the Nexus are compatible with the PDU (eg. NEMA L6-20, L6-30, C19/C20 etc.)

Conclusion:
             To ensure that your Nexus 7000 installation goes smoothly, it is important to do all the due diligences on the rack and PDU selections as well as knowing your power source and connector types.

Additional Resources:
            Cisco Nexus 7000 Series Site Preparation Guide
            Cisco Nexus 7000 Series Hardware Installation and Reference Guide
            Cisco Nexus 7000 Series Power Supply Modules

Author: Metha Chiewanichakorn , CCIE#23585 (R&S/Security/Service Provider)