The SharePoint diagnostic tool (SPDiag) is included in the Microsoft SharePoint Administration Toolkit. It comes in handy when analyzing and troubleshooting SharePoint implementations.

Copied from the tothesharepoint blog – http://blogs.technet.com/tothesharepoint/archive/2009/02/05/3197739.aspx:

“With SPDiag, you can:

• Collect IIS and ULS log files, performance counter data, event logs, and WMI instrumentation data from a SharePoint farm.
• Filter data to show granular information related to specific servers, Web applications, HTTP requests, event IDs, URI queries, and almost any other data points captured through supported channels.
• Create custom reports that can help reveal performance trends over time.
• Create snapshots of your SharePoint farm that include detailed information about your farm’s hardware, installed software and logical topology.
• Export collected data and reports that can be sent to Microsoft support personnel.”

Get the toolkit here:

• Microsoft SharePoint Administration Toolkit v3.0 x86: http://go.microsoft.com/fwlink/?LinkId=141504
• Microsoft SharePoint Administration Toolkit v3.0 x64: http://go.microsoft.com/fwlink/?LinkId=142035