Payoffs and Pitfalls of iSCSI

The draft standard for iSCSI storage networking isn't final yet, but that hasn't deterred early adopters like John Flynn from experimenting with IP storage-area networks (SAN) based on the still-emerging technology.

"It meets our needs more than the Fibre Channel architecture does," says Flynn, IT director at Minneapolis-based NRG Energy Inc. Instead of creating a new network infrastructure, the energy supplier can run iSCSI over its existing copper cabling and Cisco Catalyst 6500 Gigabit Ethernet switches.

"I'm saving $50,000 to $100,000 on a half-million-dollar effort," Flynn says, mostly from not having to buy Fibre Channel host bus adapters and switches. But more efficient management is the primary benefit, he adds, noting that network administrators can manage the SAN using existing IP-based tools. "Fibre Channel isn't integrated into the network. [It's] like small islands that you aren't able to monitor as easily," he says.

Flynn's primary issue with his IP SAN pilot is performance. He's using Cisco Systems Inc.'s SN 5420 iSCSI/Fibre Channel storage router to connect Fibre Channel storage arrays from Irvine, Calif.-based Procom Technology Inc. to about 30 servers on a Gigabit Ethernet LAN. He also plans to use iSCSI to replicate data across a Gigabit Ethernet link to another storage array in an adjacent building.

On the server side, TCP/IP processing overhead can bog down CPU performance as traffic increases.

"I've heard we can expect a performance hit of about 10% to 20%" Flynn says.

Vendors are preparing specialized iSCSI TCP off-load engines (TOE) to improve performance, but Flynn says he thinks he can get by without TOEs on his application servers, which include e-mail and a J.D. Edwards & Co. enterprise resource planning application that he says aren't storage-intensive. "If I have to put iSCSI host bus adapters in my servers, then my savings go way down," he says. So far, CPU utilization has varied by 3% to 7% during initial testing—an acceptable range.

Flynn's biggest obstacle so far has been performance problems with the SN 5420 storage router, which converts Fibre Channel protocol to iSCSI. New drivers from Cisco seem to have improved the performance, but Flynn says he's prepared to try a competing router if things don't work out.

And in the worst case?

"Our final fallback plan is to go to Fibre Channel," he says.

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Copyright © 2002 IDG Communications, Inc.

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