There are a number of items you can restrict with regards to size in a domain although you can not place a restriction on the size of the domain itself. Perhaps the most useful setting to restrict disk space is the Maximum Account Size setting. This can be set at any of System, Domain or User levels. If it is set you can be sure that the disk space sued by a domain will not exceed that of total number of users multiplied by Maximum Account Size.
Keywords:domain, size, restrict, account, maximum