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Check Disk I/O Subsystem for I/O Delay Problems

This rule checks the event log for error message 833. This message indicates that SQL Server has issued a read or write request from disk, and that the request has taken longer than 15 seconds to return. This error is reported by SQL Server and indicates a problem with the disk I/O subsystem. Delays this long can severely damage the performance of your SQL Server environment.

Troubleshoot this error by examining the system event log for hardware-related error messages. Also, examine hardware-specific logs if they are available.

Use Performance Monitor to examine the following counters:

  • Average Disk Sec/Transfer

  • Average Disk Queue Length

  • Current Disk Queue Length

For example, the Average Disk Sec/Transfer time on a computer that is running SQL Server is typically less than 15 milliseconds. If the Average Disk Sec/Transfer value increases, this indicates that the disk I/O subsystem is not optimally keeping up with the I/O demand.

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