Perfmon utility not perfect monitor of data change rates

Microsoft's Perfmon utility has limitations when it comes to helping users determine how much bandwidth they'd need to send data to their disaster recovery site. So MiraLink wrote its own utility, Data Rate Management Log, to measure change rates.

When it comes to managing data change rates over time, Microsoft's Perfmon utility is an unreliable tool, says Ron McCabe, CEO and founder of MiraLink Corp., a developer of remote mirroring appliances for Windows environments.

McCabe became aware of Perfmon's limitations when customers evaluating his company's Data Replication Engine remote mirroring appliance tried to use Perfmon to determine how much bandwidth they would need to send data to their disaster recovery site. With write logging turned on, "basically, Perfmon would quadruple every write," he says.

"Perfmon is always way off," agrees Pete Stagman, IT director at Bay State Integrated Technology, a consulting firm in Lakeville, MA. "It's like the 'Microsoft minute' when you download a file. You say to yourself, 'That can't be right.'"

In addition, Perfmon kills performance, says McCabe, by 25% to 75% -- depending on your data change rate. Ironically, the bigger the server's workload, the more of a drain Perfmon is on the server's performance.

MiraLink's solution was to write its own utility to measure change rates. But instead of running it in memory, the company deployed it external to the system. The utility, which became available this week, is called Data Rate Management Log (DRML). It runs on a 256MB USB thumb drive and retails on MiraLink's web site for $99.95. That price includes up to one hour of consulting time with MiraLink to analyze the data they've collected. MiraLink is also looking to sell DRML through its resellers and through distribution channels.

According to McCabe, the problems with Perfmon are well-documented and known to Microsoft. But the company hasn't shown any interest in improving on it. "Their attitude is, basically, that this is a free utility."

Microsoft was contacted about this issue, but did not respond by press time.

McCabe sees plenty of other application for DRML besides sizing a remote mirroring application. For example, an admin could use it to determine whether to by a Fibre Channel or IP SAN. "Once you have a SAN, you can use its tools to measure your data rates, but when you're just thinking about moving from DAS to SAN, there really aren't any other tools you can use," he says. "It's a real catch-22."

James Opava, database administrator with iHost Solutions, a web hosting and consulting firm in Columbus, OH, uses DRML for yet another purpose: monitoring the company's SQL Server databases. "It's non-intrusive," he says. "You can plug it in and it starts working without having to reboot the system. Then, at the end of the week, you just take it out and you have this nice report." Opava received DRML when evaluating MiraLink's remote mirroring, which, he says has since "been put on the back burner."

But DRML has become an important part of Opava's toolbox. "Knowing what I know now, I would definitely spend the $99 bucks on it," he says.

About the author: Alex Barrett is Executive Editor of TechTarget's Storage Media Group. .

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This was first published in July 2006

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