Top of Rack Vs. End of Row - Data-center Architecture

What is TOP OF RACK (TOR)?

In TOR, there is one or two access switch installed on the top of each server rack which provides servers network connectivity and then that access switch has the connections towards the aggregation switch which is located in the Network Rack. Hence there are only few cables going from server Rack to the network Rack.

Advantage:-

·         Cabling Cost: - It reduces the cable requirement as all servers connections are terminated to its own Rack. And hence there are only few cables running between the server and network racks.

·         Cable management: - Less resources and skills are needed to manage the cabling infrastructure.

·          Easy management and changes: - Since very less number of cable running between server and network rack, it is quite easy to locate the cable and make changes.

Disadvantage:-

·         Switch management: - As each Rack requires one or two local switches, the management of the switch becomes an overhead. It requires not only extra IPs but also management tool that manages inventory and configuration of the devices. Tools have its own capability to monitor the maximum number of devices. More devices in the network, more license cost etc.

·         Network resources: - As there are more managed devices, it require more network resources to manage the infrastructure. 

·         BW requirement:- This is only for the legacy environment where 10/40/100 Gig links are not present. As there are only few uplink available to access switch there can be issues with the BW available.

·         More rack space: We require more rack space to install SAN and LAN switches in the server rack. It in turns increases the overall Rack requirement.

·         More Space in Datacenters: - As the space requirement is very critical and expensive criteria to datacenter design and we always try to make our DC compact and efficient. As stated above more rack space can increase DC space requirement.

What is END OF ROW ( EOR )?

In EOR, all the network switches are placed in network rack only whereas cable from each server, located in server racks, runs towards the network rack.

Advantage:-

·         Less device count: - As we needn’t to install switches in each rack, the number of required switches reduces. In TOR, each rack must have a switch whether the rack is fully loaded or not, that reduces the device count.

·         Rack space: - As the overall device count reduces and hence it requires less space.

·         Cooling requirement:- Less devices in datacenter, less is the Cooling requirement. It also reduces the electricity bills and resources needed to maintain the DC environment.

Disadvantage:-

·         Inefficient Layer 2 traffic: - We all know that traffic from East to west is more than top to bottom. In EOR design, if two servers in same rack and vlan need to talk to each other, the traffic will go to the aggregation switch in network rack and then comes back. And hence reduces the efficiency.

       Similarly in case of TOR, traffic could easily and efficiently switched by the local switch present on the server rack. It could not only reduce the traffic on uplinks but also saves CPU and memory consumption of the aggregate or core switches.

·         Cable requirement: - As cable runs between each server and network switch, located in different racks, increases of cable requirement and add cost to the deployment and maintenance.

·         Cable management: - More resources and skill required for cable management. It increases the overall budget of the project.

·         Time to make changes: - As more cabling infrastructure is involved, modification not only becomes tedious but also require more time.