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Force10 data center switch delivers impressive performance

Extensive testing of 48-port, 10Gigabit switch uncovers ASIC-related anomalies, software limitations

By , Network World
March 21, 2011 12:08 AM ET

Network World - High port density, high throughput, and very low latency are bedrock requirements in the data center, and Force10's new S4810 top-of-rack switch delivers on all three counts.

Force 10 switches are in some of the world's fastest supercomputers | How we conducted our test

At the same time, Clear Choice testing revealed some interesting limitations in the "merchant silicon" chips increasingly seen in data-center switches. Tests turned up anomalies in the areas of cut-through latency; media access control address learning; and link aggregation failover handling. Beyond the switching silicon, the S4810 also turned in mixed results in multicast scalability.

The S4810 is a 1U top-of-rack switch with multiple interface options. It has 48 SFP+ ports for 1G/10G Ethernet (we tested it with 48 10G Ethernet transceivers) and four QSFP+ ports for 40G uplinks. With 10GBase-SR transceivers, the switch drew 202 watts when idle and 219 watts with its data plane fully loaded.

The switch runs the Force10 Operating System (FTOS), which includes a command-line interface (CLI) that's nearly a clone of Cisco's IOS. Experienced Cisco users will have no trouble configuring and managing this switch.

Although we tested the switch as a layer-2 data center device, it also supports layer-3 features, including major IPv4 routing protocols and static routing of IPv6 traffic, via a $2,000 software upgrade.

Significantly, the switch does not yet support some key data center protocols, according to a features questionnaire completed by Force10. These include the data center bridging extensions (DCBX); IEEE 802.1Qbb priority-based flow control (PFC); 802.1Qau congestion notification; and 802.1Qaz traffic shaping. Force10 says these features are slated for third-quarter 2011 release. (Click on links for features questionnaire and test results spreadsheet.)

Unicast performance

We used the same methodology to test the S4810 as in our January 2010 comparison of 10G Ethernet top-of-rack switches. The only difference this time was that we used 48 instead of 24 ports in measuring layer-2 unicast and multicast performance.

The S4810 put up solid numbers when it comes to basic unicast traffic handling. It delivers line-rate throughput, regardless of unicast frame size. Better still for delay-sensitive applications, the S4810 offers sub-microsecond average latency when configured in store-and-forward mode. This is one of the first store-and-forward switches we've tested to break the microsecond barrier.

We expected average latency to be lower still with the S4810 configured as a cut-through device, but that wasn't always the case. For frame sizes of 256 bytes and larger, cut-through latency was significantly higher than the equivalent test in store-and-forward mode. Further, cut-through latency increased with frame length.

Usually cut-through devices usually have two properties: They tend to be very fast (since they start forwarding a frame before it's fully received, unlike store-and-forward devices which wait until the entire frame is cached before switching it) and they have roughly the same average latency regardless of frame length.

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