Theoretically? Literally like a billion, if your hardware will support it.
Active Directory Performance Testing Tool (ADTest.exe)
ADTest.exe is an Active Directory load-generation tool that simulates
client transactions on a host server to assess the performance of the
Microsoft® Active DirectoryT within Microsoft® Windows® Server 2003 and
Microsoft® Active Directory Application ModeT.
Quick Info
File Name:
adtest.msi
Download Size:
1072 KB
Date Published:
10/7/2003
Version:
5.2.3790.1064
Overview
ADTest is an Active Directory load-generation tool. It allows
you to simulate client transactions on the host server. By varying client
load, you can relate the transaction rate to resource utilization on the
server and get some idea about the requirements for your environment.
Because ADTest can perform generic Active Directory requests, it can also
create an organizational unit structure inside Active Directory. You can add
many organizational units and user objects in those ADTest-created
organizational units. You can also add attributes to the user objects. Once
you have created the Active Directory structure you require, you can use
ADTest to perform various Active Directory requests, including Modify and
Search. Several pre-built tests have been written to reproduce some typical
activities you might want to evaluate. Examples of these pre-built tests
are: an interactive logon, a batch logon, a search for a random user, and a
modification of an attribute of a random user. By varying your hardware
environment or other test parameters, you can gain insight into the
performance sensitivities of your particular setup.
http://www.microsoft.com/downloads/...3f-92ce-4871-b8a4-99f98b3f4338&DisplayLang=en