time-taken

The "time-taken" field in IIS logs can be useful for figuring out whether your web site is performing as well as expected. Starting with IIS6, this value includes the time for the response to be fully received by the client, unlike in previous versions of IIS. Note that in IIS6 this field is not enabled by default in the IIS logs so it is worth enabling it. To do so, go to the "Web Site" tab of the properties dialogue for the site and next to the "Active Log File Format" combo box click the "Properties" button:

 

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Then when the "logging properties" dialogue comes up, make sure the "time-taken" entry is checked:

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A recently published article talks in more detail about what is included and when in the time-taken value:

Description of the time-taken field in IIS 6.0 and IIS 7.0 HTTP logging

HTH

Doug