Is there any free tools out there that can help to better document at datacenter, for information like servers in a rack, the group port it is connected to and etc?
closed as off topic by Chris S Aug 26 '12 at 4:08
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Check out RackTables: http://racktables.org/
We're using MediaWiki  in our company, works really well for internal documentation. Powers wikipedia as well.
You can use nVentory - Ruby on Rails Datacenter Inventory Manager.
You can also look at http://projects.autonomy.net.au/hotwire. It's a network and DC-aware inventory tool for servers, racks and peripherals.
If it's a Windows environment, configuration documentation can be produced automatically and nicely formatted by SYDI - sydiproject.com
Rackmonkey does the basic rack-part ok. (unless you have blades)
If you want to document more you could use GLPI: http://www.glpi-project.org/?lang=en which has a rack plugin. You can document servers, switches and devices without the plugin.