Wednesday, October 29, 2014

Theia: (Simple and Cheap) Networking for Ultra-Dense Data Centers

Paper Title: Theia: (Simple and Cheap) Networking for Ultra-Dense Data Centers

Authors: Meg Walraed-Sullivan, Jitu Padhye (Microsoft Research), Dave Maltz (Microsoft)

Presenter: Meg Walraed-Sullivan

Paper Link: http://conferences.sigcomm.org/hotnets/2014/papers/hotnets-XIII-final152.pdf

     Ultra-Dense Data Centers UDDCs are expensive to build, therefore, more CPUs are packed into a rack, which poses a number of challenges: 1) power and cooling 2) failure recovery , 3) tailoring applications 4) networking problem. This talk focuses in networking problem raised from packing a huge number of CPUs into a rack. Theia suggests we rethink the ToR architecture used in many data centers that doesn't scale to connect thousands of CPUs. We should get rid of star topology for fixed direct connect topology. The upside is that it is way cheaper, reduces the power requirement significantly and requires smaller physical space. However, this cause a lose of full bisection bandwidth and constraints the flexibility of the topology. Theia suggests replacing switches with patch panels for connectivity among sub-racks and to the rest of the data center. It is clear that over-subscription is unavoidable.
    We require a direct topology that minimizes the through traffic and supports a wide range of graph size. The best fit is circular graph but it might not be the best options. 

Questions:

Q: what is the topology of  between the racks ?
A: Imaginary. We don't have a DC yet

Q: Different racks should be able to make different trade offs? What do you think about having heterogeneous racks.
A: It's hard to do it, but we might consider it.

Q: At this scale, don't you think you need clever replacement as oversubscribe is unavoidable?
A: We need clever placement, we do it today. We will keep it in mind.