Additional Criteria for Switch Selection
Determining
the required data center latency characteristics of an Ethernet switch,
especially in HPC environments, is the first important step in choosing
a suitable switching platform. Some other criteria important in
selecting an Ethernet switch are briefly summarized here.
• Function:
After determining the required function of the switching platform,
enterprises must make sure that the switches being considered satisfy
all those requirements, functional as well as operational, without
decreasing performance or increasing latency.
For example, features such as Internet Group Management Protocol Version
3 (IGMPv3) snooping, if required, must be supported with no performance
decrease. Similarly, enterprises should thoroughly investigate a
switch's capability to support IP addresses and TCP/UDP port numbers for
load balancing across a PortChannel. For instance, packet filtering
that goes beyond MAC-level ACLs, such as IP address and UDP/TCP port
number filtering, may be required.
Enterprises should also be sure that vendors support sophisticated
monitoring and other troubleshooting tools, such as the capability to
debug packets within the switch and tools that check the software and
hardware functions of the switch while it is online in a live network.
The capability to monitor hardware and software components to provide
e-mail-based notification of critical system events may be important as
well.
• Performance:
To meet connectivity and application requirements, a switch must either
support wire-rate performance on all ports with the desired features
configured or be oversubscribed and have lower performance thresholds,
which is a viable option so long as the performance limitations are well
understood and acceptable.
• Port Density:
Satisfying the functional and performance requirements with the minimal
cost-effective number of switches is important, especially in
low-latency HPC environments, where applications will run on servers
within (ideally) a single switch.
• Cost:
The total cost of running and supporting a switch in the data center
needs to be considered. The cost must incorporate not just the price of
the switch itself, but also the expenditures necessary to train the
engineering and operations staff. Enterprises also need to consider the
availability of sophisticated proactive and reactive monitoring tools
and their overall effect on reducing the time needed to troubleshoot and
fix any problem that may occur.
Examples of Cisco Low-Latency Layer 2 Switches
The
Cisco Nexus 5000 Series access-layer switch is an example of a
low-latency cut-through single-stage fabric implementation that will
meet the requirements of all except ultra-low latency applications. The
Cisco Nexus 5000 Series uses VOQs to minimize port contention.
Another
platform that meets most low-latency application requirements is the
Cisco Catalyst® 4900M Switch, a store-and-forward switch that fits in
the data center access and distribution layers. The Cisco Catalyst 4900M
uses a shared-memory architecture with an ultra-low-latency ASIC
design.
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