Yes, ladies and gentlemen, the old oversubscription dilemma. What to think about when planning a data center deployment...
No doubt it is difficult to come up with a rule of thumb or some canned answer with regard to OSRs. There are so many variables: the characteristic of the applications running on the compute platforms, client expectations, application tolerance to delay and retransmissions, quality of service, importance of the application in terms of mission criticality, host virtualization and the number of virtual machines running on the platform...I'm sure there are more, but you get the point, I'm sure.
In a classic hierarchical data center model, the access layer's OSR has typically been higher than at the aggregation and core layers for obvious reasons. As you go north in the layered model, the switching platforms have to handle more aggregated traffic. The advent of 10GE between layers has improved the OSR at each layer most notably at the access layer. But it's a double-edged sword, isn't it? This improvemnet is only temporal as the link speed and offered data rates from server to access layer are also increasing. 10GE between server and access has once again raised the OSR. This pendulum should once again swing in the direction of more favorable OSRs with the advent of 40 and 100GE between switching layers.
On this board, there are many seasoned professionals who have had to negotiate this challenge in the past and present. I am curious to know what metrics were used during the planning phase of your new data center deployment and what thought leadership did you bring to the table - or perhaps experienced from others. With all the variables one must take into account, is there indeed a best practice that loosely takes these variables into consideration and allows for an accepted starting point? Sure, we would all love that golden 1:1 ratio, but how far from this ideal mark is acceptable?
I would love to hear some thoughts.....
I know this is can make for a tedious discussion, so it's not for the faint hearted. :-)
Regards
Victor
