Data Center Architectures Overview
Explore traditional data centers, limitations like oversubscription and fault tolerance, scalable commodity network architectures, history lessons on Clos networks, and the fat-tree architecture in this informative lecture material that covers various design aspects and considerations for efficient data center setups.
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Data Center Architectures CIS 700/005 Lecture 2 Includes material from lectures by Hakim Weatherspoon and Jennifer Rexford
Traditional Data Centers Internet Data Center Layer-3 router Core Aggregation Layer-2/3 switch Layer-2 switch Access Servers
Limitation (1): Oversubscription Ratio of the worst-case achievable aggregate bandwidth among the end hosts to the total bisection bandwidth of a particular communication topology Lower the total cost of the design Typical designs: factor of 2:5:1 (400 Mbps)to 8:1(125 Mbps)
Limitation (2): Fault tolerance Oversubscription + Bigger routers less routers at the top of the tree a core router failure has high blast radius
A Scalable, Commodity Data Center Network Architecture Mohammad Al-Fares, Alexander Loukissas, Amin Vahdat Scalable interconnection bandwidth 1:1 oversubscription Economies of scale Backwards compatibility
History Lesson: Clos Networks (1953) Emulate a single huge switch with many smaller switches Add more layers to scale out
History Lesson: Clos Networks (1953) Emulate a single huge switch with many smaller switches Add more layers to scale out
History Lesson: Clos Networks (1953) Emulate a single huge switch with many smaller switches Add more layers to scale out
Fat-tree Architecture K-ary fat tree: three-layer topology (edge, aggregation and core) each pod consists of (k/2)2 servers & 2 layers of k/2 k-port switches each edge switch connects to k/2 servers & k/2 aggr. switches each aggr. switch connects to k/2 edge & k/2 core switches (k/2)2 core switches: each connects to k pods
Obligatory Network Questions How do I address destinations? Hierarchical IP addresses for scalability [PodNumber].[SwitchNumber].[Endhost] How does a switch route packets? Assumption: every routing table entry has 1 output Route downward using prefix (for scalability) Route upward using suffix (for load balancing)
Routing Optimizations 1. Flow classification Classify flows (e.g., src, dest, port #s) Move around a small set of flows as needed 2. Flow scheduling Keep track of large, long-lived flows at the edge switches Assign them to different links
VL2: a scalable and flexible data center network A. Greenberg, J. R. Hamilton, N. Jain, S. Kandula, C. Kim, P. Lahiri, D. A. Maltz, P. Patel, and S. Sengupta Let s take the single big switch model to the limit: Uniform high capacity Performance isolation: Layer-2 semantics:
Virtual Layer 2 Switch (VL2) 1. L2 semantics 2. Uniform high capacity 3. Performance isolation
VL2 Goals and Solutions Approach Solution Objective Name-location separation & resolution service 1. Layer-2 semantics Employ flat addressing 2. Uniform high capacity between servers Guarantee bandwidth for hose-model traffic Flow-based random traffic indirection (Valiant LB) Enforce hose model using existing mechanisms only 3. Performance Isolation TCP Hose : each node has ingress/egress bandwidth constraints
