Distributed elements, in any sector, have their basic benefits and drawbacks compared to a single large tool. It is similar to the preference of using small aircraft over a jumbo 747 for carrying passengers between proximate airfields or to using a bus vs. multiple private cars to move a football team around.
In networking, the analysis between a Virtual Modular Switch (VMS) and a Modular switch is cost and performance driven. A network facilitator will prefer a solution that gets the job done at the lowest cost. Such an analysis will produce different results based on the cluster’s size. If the number of network ports required for the solution can be fitted into a single chassis based device, this means that the use of the chassis, although equipped with redundant peripheral elements such as fans and power units, is presenting a single point of failure in the network. In order to solve this, a second chassis is introduced for sharing the load and provide connectivity in case of chassis failure.
From a financial point of view, assuming you had a chassis of 1000 ports in full use, you need to deploy a solution of 2000 ports for high availability purposes which means a 100% price increase. Using 2/3 of the ports in the chassis will translate to 200% increase on top of the real required investment and more such examples are easy to find. Other problem with the chassis is that it comes in very few form factors so if your solution requires 501 ports while the chassis of choice supports 500, you need to add another and pay the double cost.
Alternatively, breaking the solution into multiple devices in a VMS gives both improved granularity in terms of port count and high availability in terms of impact from failure. In loose terms, if the VMS consists of 20 switches, the failure of a switch translates to 5% loss of network capacity. Regardless from how powerful and complicated the chassis is, this is a classic case where the strength of many tops the strength of one.
The same logic applies when the size of your network grows and gets to the point when multiple modular switches are needed due to very large scale. Assume a network that requires 5000 ports while the chassis of choice carries 500, this will translate to 10 modular switches in the implementation so even if an additional chassis will be added to improve high availability or one will fail, the impact on the network will loosely be translated to a 10% delta. Doing the same with a VMS type of a solution will result is deploying ~200 routers in a network with a benefit which is not necessarily worth it.
One more observation that should be noted is the fact that managing that many devices can become a challenge. However, looking at the wider picture, I don’t see this as a differentiator between deploying a VMS or a chassis (one or many). Take into account that the VMS or chassis is merely the aggregation solution of the network, meaning it is connected to numerous access switches or top of rack switches in case of a data center implementation.
This means that the management challenge exists for hundreds of elements before the aggregation solution come to the picture. Eventually the delta in the number of elements to manage comes down to ~200 vs. 220 in small clusters or between 2000 vs. 2200 in huge networks so as I said, not a real differentiator.
Stay tuned to further exploration of the Mellanox implementation of VMS. Later…
Author: Since 2011, Ran has served as Sr. Product Manager for Ethernet Products. Prior to joining Mellanox, Ran worked at Nokia Siemens Networks as a solution sales and marketing specialist for the packet networks business unit. Ran holds a BSc. In Electrical Engineering and Computer Sciences from the University of Tel Aviv, Israel.