More evidence of an overload came in a buffer-overflow message we saw when running this test (and the group capacity test) immediately after a switch reboot. The fact that the switch did not display this message on the second and subsequent test iterations suggests an issue with initial loading of a multicast software module into memory when large group counts are involved. Another issue we saw (on all iterations, not just the first one) is that the switch's CLI erroneously reported the same port twice as a member of a given multicast group.
Force10 said it replicated these results in-house, and found much lower join and leave times - of 1 second or less - when 100 groups were involved instead of nearly 1,000. The vendor also says it's doing more optimization work on this new platform.
The final set of multicast tests examined switch throughput and latency, again using 989 groups. In these tests, we configured the Spirent TestCenter traffic generator to transmit multicast traffic to one port, and act as multicast subscribers on the 47 remaining ports.
The switch offered line-rate throughput of multicast traffic, with the exception of jumbo frames. With these 9,216-byte frames, the highest zero-loss rate was roughly equivalent to around 98.5 percent of line rate. That's a bit of a surprise in that most data-center switches deliver line-rate throughput in all cases, unicast and multicast alike. On the other hand, jumbo frames are common for unicast than multicast transport (think backup and disaster-recovery applications); thus, the multicast jumbo throughput result probably isn't a concern for most users.
Average and maximum multicast latencies were roughly comparable to unicast with the switch in store-and-forward mode.
For network managers whose foremost switch requirements are high port density and very low latency, the S4810 is a good fit. The S4810 still has more work to do in the areas of data center features support and multicast processing speeds. These involve software fixes, and Force10 says they're already in the works. Hardware anomalies, such as those involving MAC address learning and link aggregation failover, are harder to fix and may take longer to address.
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