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

Topic Status: Some information in this topic is preview and subject to change in future releases. Preview information describes new features or changes to existing features in Microsoft SQL Server 2016 Community Technology Preview 2 (CTP2).

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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