Data Center Switches Promise Convergence

Data centers usually contain at least two separate networks: Fibre Channel for storage and Ethernet for data traffic—that is until 10G Ethernet switches were introduced. Computer World discusses data center switches and the different approaches to convergence.

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Fibre Channel and FCoE have stringent loss and delay requirements. Both use a credit-based system in which loss should never occur. Contrast that with Ethernet, which is stateless and doesn't attempt to retransmit lost frames. Further, Fibre Channel and FCoE require deterministic (predictable) latency and jitter; Ethernet doesn't.

To accommodate storage traffic on Ethernet, the IEEE has developed new mechanisms that aim to deliver Fibre Channel-like service levels over Ethernet. The most important of these is priority-based flow control (PFC), described in IEEE 802.1bb and supported by the Blade, Cisco and Dell switches. PFC extends Ethernet flow control to work on a per-VLAN priority basis instead of a per-port basis. One or more of those priorities can carry storage traffic.

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