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Some of the novelties of iSCSI are related to the nature of the IP protocol. While the FC protocol is optimized for networks dedicated to connecting servers to arrays, IP-based iSCSI SANs may have to compete with nonstorage IP traffic. To minimize the impact of disruptive IP traffic, data center managers are isolating iSCSI traffic from nonstorage traffic via dedicated iSCSI networks that have no physical connection to the rest of the network, or leveraging Ethernet isolation techniques like access control lists and Virtual LANs (VLANs). "To avoid interferences from the in-house LAN, we decided to run our iSCSI network on a standalone Foundry Networks Inc. FastIron 48-port Ethernet switch," reports Kevin Mount, senior network administrator at Spokane Public Schools in Washington.
Although physical and virtual segregation greatly enhance security and performance, storage managers may need to resort to advanced Ethernet techniques like Ethernet jumbo frames and enabling flow control on the network switch and adapters to alleviate congestion and optimize throughput. In cases where the bandwidth of a single gigabit link doesn't suffice, multiple links may have to be combined into a single aggregated link by taking advantage of Ethernet trunking or link aggregation; this can sidestep the need to deploy an expensive 10Gb Ethernet infrastructure to overcome bandwidth limitations.
On the host-side, TCP offload engines (TOEs) and iSCSI HBAs can
In mixed-protocol environments, storage managers need to be aware of Ethernet oddities like erroneous speed/mode autonegotiations between Ethernet switches and network interface cards (NICs) because they can have a detrimental impact on iSCSI network performance. "To eliminate the possibility of autonegotiation problems, we hardcode all switch and server Ethernet ports," says Mount.
This was first published in February 2007