Forthe 6200 series fabric interconnects running Cisco UCS Manager, version 2.0 and higher, Ethernet uplink
portsand Fibre Channel uplink ports are both configurable on the base module, as well as on the expansion
module.
Forexample, if you havetwo Cisco UCS 5100 serieschassis that are fully populated with half width Cisco
UCSB200-M1 servers, you have16 servers.In acluster configuration, with one LAN uplink per fabric
interconnect,these 16 servers share 20GbE of LAN bandwidth. If more capacity is needed, more uplinks from
thefabric interconnect should be added. We recommend that you have symmetric configuration of the uplink
incluster configurations. In the same example, if 4 uplinks are used in each fabric interconnect, the 16 servers
aresharing 80 GB of bandwidth, so each has approximately 5 GB of capacity. When multiple uplinks are
usedon a CiscoUCS fabric interconnect the network design team should consider using a port channel to
makebest use of thecapacity.
Number of Uplink Ports from I/O Module to Fabric Interconnect
Youcan choose to add more bandwidth between I/O module and fabric interconnect by using more uplink
portsand increasing the number of cables. In Cisco UCS, you can have one, two, or four cables connecting
aI/O module to a Cisco UCS 6100 series fabric interconnect. You can have up to eight cables if you're
connectinga 2208 I/O module and a 6248 fabric interconnect. The number of cables determines the number
ofactive uplinkports and theoversubscription ratio.
Number of Active Links from Server to Fabric Interconnect
Theamount of non-oversubscribed bandwidth available to each server depends on the number of I/O modules
usedand the number of cables used to connect those I/O modules to the fabric interconnects. Having a second
I/Omodule in place provides additional bandwidth and redundancy to the servers. This level of flexibility in
designensures that you can provide anywhere from 80 Gbps (two I/O modules with four links each) to 10
Gbps(one I/Omodule with onelink) to thechassis.
With80 Gbps to the chassis, each half-width server in the Cisco UCS domain can get up to 10 Gbps in a
non-oversubscribedconfiguration, with an ability to use up to 20 Gbps with 2:1 oversubscription.
Guidelines for Estimating Oversubscription
Whenyou estimate the optimal oversubscription ratio for a fabric interconnect port, consider the following
guidelines:
Cost/Performance Slider
Theprioritization of cost and performance is different for each data center and has a direct impact on the
configurationof oversubscription.When you planhardware usage for oversubscription,you needto know
wherethe data center is located on this slider. For example, oversubscription can be minimized if the data
centeris more concerned with performance than cost. However, cost is a significant factor in most data centers,
andoversubscription requires carefulplanning.
Bandwidth Usage
Theestimated bandwidth that you expect each server to actually use is important when you determine the
assignmentof each server to a fabric interconnect port and, as a result, the oversubscription ratio of the ports.
Foroversubscription, you must consider how many GBs of traffic the server will consume on average, the
ratioof configuredbandwidth to used bandwidth, and thetimes when high bandwidthuse will occur.
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Traffic Management