Although this report is not a full performance benchmark, several performance measurements were taken using various network adapters with the same I/O workloads.
Ethernet network adapters are one important component of an iSCSI storage solution. It should be noted that best practices recommend that a true server-class network adapter should be used for iSCSI storage applications. The low-cost network adapter listed below that was used in these tests is not a true server-class network adapter, but was used only as a point of reference. This truly shows the importance of server-class network adapters in iSCSI deployments.
Three different types of Gigabit Ethernet network adapters were used for these tests. Two low-cost network adapters were deployed, each with one port. The advanced network adapter and the TCP Offload adapter are dual-port, server-class network adapters. The low-cost network adapters used in this report are available for the least cost, but are not recommended for iSCSI storage solutions. The advanced network adapters are available for a mid-range price. The TCP Offload adapters are, by comparison, more expensive. The three types of network adapters used in the Demartek lab were:
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Low-cost network adapter: NetGear® GA-311
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Advanced network adapter supporting Receive-side Scaling: Intel® Pro/1000 PT
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TCP Offload network adapter: Alacritech® SEN2002XT
The CPU usage on the dual-core, single processor server using the low-cost network adapter, without the Scalable Networking Pack was significantly skewed toward the first core with very little activity on the second core, especially during read operations. When SNP was installed and the advanced network adapter and the TCP Offload adapter were each used, the dual-core processor server exhibited a lower and more evenly balanced CPU utilization. The following Task Manager snapshots highlight the differences for light to moderate workloads using a mid-range iSCSI target solution.
Dual-core server with
low-cost network adapter
Dual-core server with
SNP and Receive-side Scaling
server-class network adapter
Dual-core server with
SNP and TCP Offload
server-class network adapter
The differences between server-class network adapters and low-cost network adapters became obvious during our tests. We found that under heavy workloads with a high-performance iSCSI target solution, the low-cost network adapter configuration became unacceptably slow, fully utilizing the processor and locking out other processes on the server including mouse and keyboard controls. The same workloads using the advanced network adapter and the TCP Offload adapter, which are server-class network adapters, completed the workloads in the expected time and did not lock out other processes.
The charts below show a representative sample of percentage of CPU utilization for the three types of network adapters. Two paths, using MPIO, were used for this sample.
Network adapter legend:
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NIC-LOW: low cost network adapter
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NIC-SVR: advanced server-class network adapter supporting Receive-side Scaling
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NIC-TOE: TCP Offload adapter supporting TCP/IP Offload Engine
Performance will vary depending on many factors, including number of processors and processor cores in the application server, amount of memory in the application server, network adapter type, specific network adapter features that are enabled, and the iSCSI target storage system characteristics.
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