What are those Exchange stats telling you?

Exchange is one of the most popular applications in the enterprise, so tuning it for best storage performance is important. To help you keep it running optimally, you should use the Performance Monitor to keep a check on how well Exchange is doing.

The most important statistics to monitor are probably current queue length, disk timer, disk-bytes-per-transfer, disk-bytes-per-second, and free megabytes. Queue length in an Exchange server should normally run about 2 or less, with the exception of the drive that contains Exchange's .edb files. Because Exchange caches transactions, that queue will usually spike every few seconds (about twice a minute).

The percent disk time counter shows how much time your drives are actually working. Ideally that should be less than 50 percent and anything above 90 percent indicates you've got a problem.

The disk bytes counters don't need to be checked as frequently. However they're important as a long-term indicator of system performance. Of course, you want as many bytes transferred per second or per transaction as possible. If this number starts to degrade over time, you need to make modifications to your Exchange storage system.

Free megabytes, the amount of remaining disk space, needs to be tracked and an alarm threshold set, so you can add disk space or make other adjustments to your log files as your logs and databases grow.

Exchange performs best if it is running on a separate

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server. If the statistics are showing signs that the system is loading up, you may want to move Exchange services to a more lightly loaded server or move some of the other services on that server to another server.

Microsoft discusses tuning Exchange Server in a series of articles on their Web site.

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.


This was first published in September 2003

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