Which networking spine-leaf decision most affects scale-out east-west traffic for a new DC build?

The oversubscription ratio between leaf and spine switches is a critical design parameter in a spine-leaf fabric. It defines the ratio of downstream bandwidth (from leaf switches to servers) to the upstream bandwidth (from leaf switches to spine switches). This ratio directly impacts the network's ability to handle east-west (server-to-server) traffic without congestion. A lower oversubscription ratio (e.g., 1:1) creates a non-blocking fabric, maximizing performance for scale-out applications, while a higher ratio can create bottlenecks, limiting the effective bandwidth available for inter-server communication as the data center grows.

A. Leaf to end-host cabling color: Cable color is used for administrative identification and organization; it has no impact on network performance, bandwidth, or traffic flow.
C. Coffee maker brand in the NOC: The brand of an appliance in the Network Operations Center (NOC) is entirely unrelated to the data center's network architecture or performance.
D. Number of floor tiles per row: While physical layout is important for cabling and cooling, the number of floor tiles does not directly determine the network's logical capacity or its ability to handle traffic.

1. HPE FlexFabric and Composable Fabric Data Center Validated Design Guide, (March 2019). In the section "Spine-and-leaf architecture," the guide states, "The ratio of downlink to uplink bandwidth is called the oversubscription ratio. This is a key design consideration when balancing cost and performance." (Page 12, Paragraph 2). This highlights the ratio as a fundamental design choice affecting performance.

2. HPE Aruba Data Center Networking Solution Guide, (April 2022). The section "Leaf-Spine Design" explains, "The oversubscription ratio is a key design consideration. It is the ratio of downstream bandwidth (to servers) to upstream bandwidth (to spines)... A 1:1 oversubscription ratio is considered non-blocking... Higher oversubscription ratios are common to reduce cost but can impact application performance if the east-west traffic patterns are not well understood." (Page 9). This directly links the ratio to east-west traffic performance.

3. Al-Fares, M., Loukissas, A., & Vahdat, A. (2008). A scalable, commodity data center network architecture. ACM SIGCOMM Computer Communication Review, 38(4), 63–74. https://doi.org/10.1145/1402946.1402967. This foundational academic paper on fat-tree topologies (the basis for spine-leaf) discusses how the structure provides uniform high bandwidth between servers, a principle directly managed by the oversubscription ratio in practical implementations. (Section 3.1, "Topology").