FREB logs are the best tool to troubleshoot compression issues on IIS 7. But before starting looking into FREB logs, it’s good to check following configuration settings in applicationhost.config file.

 

<httpCompression directory="%SystemDrive%\inetpub\temp\IIS Temporary Compressed Files">

            <scheme name="gzip" dll="%Windir%\system32\inetsrv\gzip.dll" />

            <staticTypes>

                <add mimeType="text/*" enabled="true" />

                <add mimeType="message/*" enabled="true" />

                <add mimeType="application/x-javascript" enabled="true" />

                <add mimeType="*/*" enabled="false" />

            </staticTypes>

            <dynamicTypes>

                <add mimeType="text/*" enabled="true" />

                <add mimeType="message/*" enabled="true" />

                <add mimeType="*/*" enabled="false" />

            </dynamicTypes>

        </httpCompression>

 

 

<urlCompression doStaticCompression="true" doDynamicCompression="true"

dynamicCompressionBeforeCache="true" />

 

Related Articles:

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Changes to compression in IIS 7

http://www.ksingla.net/2006/06/changes_to_compression_in_iis7/

 

Configuring HTTP Compression in IIS 7

http://technet.microsoft.com/en-us/library/cc771003(WS.10).aspx