Identifying Design Priorities

Rarely will any network architect find that every part of the Active Directory design process goes smoothly. Because the organizations are based on human wants and needs, political issues are going to arise that will cause debates over what is really required. As the designer, it is your job to separate the emotional desires from what should take priority within the design.

The interviews with key personnel should present the designer with clues as to where the organization s priorities lie. Base all of your decisions upon the priorities that you discover during these interviews. Although you may find that most of the interviews with the powers-that-be may point out that they want to keep costs at a minimum, you may find that other criteria override the cost issue. Two other priorities, high availability and reliability , can take precedence, and you will find that they are usually mutually exclusive to the cost priority.

Because highly available solutions and reliable systems are more expensive than systems that do not provide this functionality, you need to identify where the organization stands.

Using Reliable Solutions

Reliable systems usually have mechanisms put into place for redundancy. Dual power supplies , storage partitions that take advantage of stripe sets with parity or mirroring, dual backplanes , and other technologies that provide hardware solutions to achieve fault tolerance do not come cheap. Active Directory is no exception. Because all of the domain controllers within a domain replicate the database to one another, you need multiple domain controllers. This design could dictate that multiple domain controllers are placed at high-priority sites. For additional levels of reliability, make sure you identify multiple DNS servers as well as network devices that define the physical infrastructure.

Certain domain controllers should be based on reliable systems. The Operations Masters are roles that only certain domain controllers can hold. The Operations Masters provide a means of controlling certain resources so that the functionality of Active Directory is not compromised. Two of these roles are only available on one domain controller within the forest:

• Schema Master

• Domain Naming Master

The other three roles are available on one domain controller in each of the domains within a forest:

• Primary Domain Controller (PDC) Emulator

• Infrastructure Master

• Relative ID (RID) Master

Because the function of each of these domain controllers is critical to Active Directory, make sure you plan to have reliable hardware for them.

Note  

For more information on Operations Masters, check out MCSE: Windows Server 2003 Active Directory Planning, Implementation, and Maintenance Study Guide , by Anil Desai with James Chellis (Sybex, 2003).

Using High-Availability Solutions

Having systems that are highly available is also an expensive proposition. However, many companies that need their systems to be available at all times. Microsoft has clustering services available in the more expensive Enterprise and DataCenter Editions; you will not find clustering available in the Standard or Web editions. Also, several third-party high-availability solutions do exist, but again, they incur additional costs for the organization. If it is determined that a service must be available at all times, or a service level agreement has been put into place that guarantees availability of a service, cost is a lower priority than availability.

Whenever making trade-offs, make sure you include the stakeholders in the decision. You may come across instances when the designer should not make the trade-off; it should be left up to the stakeholders. For instance, if you are trying to determine what type of server solution you will use for your domain controllers, and you need the service to be reliable, you may end up with two solutions to choose from: the first solution is to use reliable hardware that has redundancy built in, and the second solution foregoes the highly reliable hardware for multiple servers to be used, one primary server and one backup. Both solutions may fit the organization s requirements, but the two-server solution may cost less than the redundant hardware requirements for the first option. Present the pros and cons of each of the solutions and allow the stakeholders to make the decision.

Design Scenario ”Priority Identification

When interviewing management staff at Premier Pawn, a pawn shop that has ventured into the world of online sales, Tanya gathered the following information:

The Chief Executive Officer spoke of how the company had grown from a single small pawn shop in a college town to a multi-state company that became very popular due to their humorous ad placements. In the past few years , they have turned to the Internet to auction items that were in their inventory. While they are not the most recognized online auction house, the auctions have proven very popular due to the fact that the clientele trusts the Premier Pawn to deliver on the sale.

The Chief Information Officer has identified two areas that they need to improve upon with the new directory service design. Since they are moving to Exchange Server 2003 and using Internet Security and Acceleration Server, they are moving to Active Directory to support the two products. They are also taking advantage of the restructured Internet Information Server 6.0 for their web services.

The CIO also noted that since they were running auctions 24 hours a day every day of the year, they needed to make sure that the systems were functioning at all times. It is estimated that if the auctions are not accessible, the company could lose an estimated $225,000 per day in revenue. The company is willing to commit the resources to make sure that the system is always accessible to the users.

1. Question: What needs are identified for Premier Pawn s Windows Server 2003 Active Directory design? Answer: Application Support and High Availability

2. Question: Which of the design needs has the highest priority when choosing tradeoffs on the design? Answer: High Availability