There is no longer an option in the SharePoint 2010 Central Administration page to "quiesce farm" as there was in SharePoint 2007.

Stsadm commands article

To quiesce SharePoint 2010, run this stsadm command:  stsadm -o quiescefarm -maxduration n

To unquiesce SharePoint 2010, run this stsadm command:  stsadm -o unquiescefarm