Testing the waters of giga-speed NICs

Ready to upgrade your servers with a brand new Gigabit Ethernet adapter? Make sure your server will know what to do with all that power. The truth is that actual application throughput on even the most powerful servers, such as a Sun UltraSparc 2 running at 533 MHz and using a Gigabit Ethernet NIC, peaks out in the 400M to 500M bit/sec range. And that's full duplex. "Killer applications" or not, operating system protocol stacks have performance limitations. Server bus contention can also erode throughput. Regardless of where the limitation lies, we have reached the age where the NIC is certainly not the bottleneck. Essentially, NIC bandwidth has surpassed the server's ability to use it.

There are still several good reasons to upgrade to a Gigabit Ethernet NIC instead of trunking two or four Fast Ethernet NICs: to keep down CPU and bus utilization, and to avoid the interoperability problems and the high cost of configuration associated with trunking. However, realize that actual application throughput doesn't necessarily equal NIC bandwidth, even if you consider physical layer and frame overhead. For instance, the bandwidth (line rate) of a Gigabit Ethernet NIC is 2G bit/sec, or 1G bit/sec in each direction. If you were to have five clients performing an FTP "get" and another five FTP "puts" on a server, the combined throughput would be less than 500M bit/sec. That's 25% efficiency (500M bit/sec divided by 2G bit/sec).

In time, faster CPUs and buses, combined with more efficient and streamlined NIC and operating system designs, will increase application throughput. For now, make sure you find out from your NIC and server vendors just what level of application throughput you can expect from a particular system, and add it to your list of considerations when deciding if and when to upgrade.

The Tolly Group, a strategic consulting and independent testing organization, offers a full range of services designed to furnish the vendor and the end-user communities with authoritative and unbiased information. The Tolly Group is a leader in assessing leading edge technologies and provides such services as: network design, product evaluations, industry studies, and market research. For more information, visit The Tolly Group's World Wide Web site, send e-mail to info@tolly.com, call 800-933-1699 or 732-528-3300, or fax 732-528-1888.

Gigabit Ethernet standard delayed at least until June
Vendors scrambling to assure customers they'll upgrade for free. Network World, 2/5/98.

Review and buyer's guide: Gigabit Ethernet switches
Network World, 1/26/98.

Review: Gigabit or ATM for the backbone?
Network World, 11/17/97.

Upgrading switch-to-server links
A before and after diagram from the Gigabit Ethernet Alliance.

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