After migrating data from SharePoint Server 2007 to SharePoint Server 2010 you might want the information to be still available on the original SharePoint 2007 but you want to avoid that they still make changes to the original content. The easiest way to do this is using
stsadm –o setsitelock http://sitecollectionurl –lock readonly
which allows you to lock one or more site collections - see Lock site collections (Office SharePoint Server) on TechNet for more information.
SharePoint Server 2010 provides you another option to do this using the Set-SPSiteAdministration PowerShell cmdlet -
Set-SPSiteAdministration -Identity http://sitecollectionurl -LockState ReadOnly