Introduction to Active Directory's Physical Structure

This video discusses the AD partitions, including the Application Partitions, Replication, AD Site Design Factors, Scheduling Replication.
This applies to Windows 2000, 2003, 2008, 2008 R2 and Windows 2012.
Compiled From MOC 2279b Planning, Implementing & Maintaining a Microsoft Windows 2003 AD Infrastructure, Module 1, by Ace Fekay, MCT, MVP: Directory Services

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AD partition:

<b>Domain partition: </b>
contains replicas of all the objects in the domain. 
The domain partition is replicated to all of the domain controllers in the same domain

<b>Configuration Partition:</b>
contains forest topology. 
A topology is a record of all domain controllers and the connections between them in a forest.

<b>Schema Partition:</b>
contains the forest wide schema. Each forest has one schema so that the definition of the each object class is consistent. 

<b>The configuration and schema partitions are replicated to each domain controller in the forest.</b>

<b> Application partitions (optional) : </b> contain objects that are unrelated to security and that are used by one or more applications. Application partitions are replicated to specified domain controllers in the forest.

 AD sites:

A site is a group of well-connected computers.
After sites are established domain controllers with in a site communicate frequently. This communication minimizes the latency within the site. Latency is the time that is required for a change that is made on one domain controller to be replicated on other domain controllers (DCs). you create sites to optimize the use of bandwidth between physically separated domain controllers.

You can configure DCs in separate sites which may be linked by sole communications to communicate only at scheduled times. You typically schedule this replication traffic when it has minimal impact on other network traffic. 

So, An organization must plan both the logical structure and physical structure to meet its needs.

Say for example,

Case 1: If your organization needs only one domain, but has offices around the world, you may decide to create multiple sites to keep the replication and logon traffic with in the site. In this case, you can configure replication between sites to occur during the hours when other network traffic is lightest. If all employees in your organization work at one location, but in departments that have different security and policiy needs, you may decide to create several domains in one site. 

Or

Case 2: If your organization has multiple locations with more than one domains represented at each location, you may decide to create multiple sites that have atleast one domain controller from each necessary domain at each site. 

Summary:


1: Domain controllers contain active directory partitions that store objects and other information.  
2: you use sites to control when and where replication and logon traffic occur.          

At the end of this presentation you will be able to: 
1. Define the elements of the physical structure of the active directory directory service, and the purpose of those elements.

2. Discuss how the logical and physical structures of Active Directory work together to meet 

organizational needs.

              ADDS (Structure)
                    /            \
                   /               \
                  /                  \
           Logical             Physical
               
 Organize and manage   enables to optimize network traffic.  
  users, groups and         Physical structure of AD define when and where                   network resources       replication and logon traffic occur. The elements of the                                             physical structure are Dc and sites.Each domain controller                                     perform storage and replication functions.
                                    The logical element of the domain is a unit of replication.                                         The physical DC contains the information that  will be                                             replicated. A DC can support only one domain.To ensure                                       continuous  availability of Active Directory, each domain                                         must have more than one domain controller.