Remember from Chapter 1 that a server farm is a logical group of MetaFrame XP servers that are managed together as one entity, similar in concept to a Microsoft Windows domain. With MetaFrame XP, one single farm can scale to hundreds of servers to support a very large enterprise. Of course, there are also reasons that organizations might choose to have multiple, smaller server farms.
When deciding on the boundaries that separate server farms, one geographic location does not always correlate to one server farm. There are many situations that call for a server farm to span multiple locations, even if those physical locations are connected via slow WAN links. Conversely, there are also reasons that one physical location would need to have multiple MetaFrame XP sever farms, or even multiple farms within one datacenter. The decision as to the number and locations of farms needs to balance technical and business requirements.
Even though we've used the analogy of Microsoft Windows domains to explain the concept of MetaFrame XP server farms, the server farm boundaries do not have to be aligned to Windows domain boundaries. One server farm can span multiple domains, or one server farm can be made up of MetaFrame XP servers that belong to different domains.
Why should you care about server farm design?
You should design you server farm boundaries independently of your MetaFrame XP server locations. This means that you should first decide where you're going to put your servers. Only then should you start to think about their farm memberships and how many farms you will have.
The decision to create one all-encompassing server farm or several smaller server farms impacts several areas in your environment, specifically:
- Ease of management.
- Network bandwidth usage.
- End users' ability to logon.
Ease of Management
All of the MetaFrame XP servers in one farm can be managed together. They are managed via the same tool, and many security and configuration settings are configured on a farm-wide basis. MetaFrame XP servers that belong to different farms must be managed separately. Applications cannot be load-balanced across servers in different server farms (although users can simultaneously run sessions on MetaFrame XP servers that are members of different farms).
Network Bandwidth Usage
MetaFrame XP servers in a server farm must communicate with other servers in the same farm. (Remember the new IMA server-to-server communication protocol?) Therefore, having many servers in a farm increases network communication overhead.
End Users' Logon Ability
One single server farm can span multiple domains. In these multi-domain farms, it is possible for one published application to be load-balanced across MetaFrame XP servers that are members of different domains. If this is the case, users may experience intermittent logon problems if they are routed to a load-balanced server from another domain that does not trust their domain.
What are the server farm design options?
When thinking about your MetaFrame XP server farm layout, there are really two choices. You can build large farms that include MetaFrame XP servers from multiple geographic areas, or you can build multiple small farms, each including a single group of MetaFrame XP servers.
Note that the "geographic area" referred to here relates to geographic area of the MetaFrame XP servers only, which is why we design the server farm after we design the placement of the MetaFrame XP servers. If you have users all over the country, but you have decided that all the MetaFrame servers will be in one location, then that would be considered a single "geographic area," in regards to server farm design.
Option 1. One Large Server Farm
There are many advantages of having one large server farm. Remember, one large server farm does not mean that all of your servers must be in the same physical location. Some companies have MetaFrame XP servers in several datacenters throughout the world, with all of those servers belonging to the same server farm.
By creating one server farm, all administration can be done by one group of people. Farm-wide changes affect all the MetaFrame XP servers in the company because all company servers are in the same farm. Additionally, each user only needs a single ICA connection license, even if they connect simultaneously to multiple MetaFrame XP servers in different parts of the world.
Unfortunately, there are also drawbacks to the single farm model. Because all farm servers need to keep in communication with each other, farms that span slow WAN links will need to use part of that link for farm communication. (A farm can be divided into logical "zones" that help manage that communication. These zones are covered in the next section.) Also, server farms are designed to be administered as a group, and this administration is "all or nothing." You can't give some people administrative rights to some farm servers while preventing them from administering others. This becomes a real issue if you have farms that span great distances and you want local administrators to be restricted to managing local servers only.
Advantages of Creating One Large Server Farm
- Efficient license usage.
- Single point of administration.
Disadvantages of Creating One Large Server Farm
- Cannot segment farm server administration.
- Intra-farm network communication.
- All farm-wide settings must apply to all servers.
Option 2. Multiple Smaller Server Farms
Many companies choose to segment their MetaFrame XP servers into multiple farms. Again, this segmentation does not have to follow geographic boundaries. Some companies have several server farms for MetaFrame XP servers that are in the same datacenter because different departments have different needs, users, and servers.
Splitting your MetaFrame XP environment into multiple farms allows local groups or departments to manage their own servers and to purchase and manage their own licenses. Larger companies with several locations can save WAN bandwidth by keeping MetaFrame XP servers on both sides of the WAN in separate farms.
Of course, if separate farms are created then one user connecting into multiple farms will need a MetaFrame XP connection license for each farm that is used. (See Chapter 14 for full license usage details.) Also, any enterprise-wide changes made by MetaFrame XP administrators will need to be manually configured for each farm.
Advantages of Creating Multiple, Small Farms
- Intra-farm network communication is not as broad.
- Departmental licensing.
- Local administration.
- Different farms can have completely unrelated configurations and settings.
Disadvantages of Creating Multiple, Small Farms
- One user connection to multiple farms requires multiple licensees.
- Enterprise-wide configuration changes need to be separately applied at each farm.
Considerations when Designing your Server Farm
There are several considerations that will help you make your decision as to whether you will have one large farm or several smaller farms. If you choose to have several smaller farms, these can also help you choose your farm boundaries and how you should segment your server farms.
- How will your MetaFrame XP servers be administered?
- How much network bandwidth is available?
- What are your licensing requirements?
- What is the Windows domain / Active Directory design?
- Where are the users located?
The desired administration of your MetaFrame XP environment will drive the server farm design. A MetaFrame XP server farm is designed to be managed as one group. Because of this, any farm administrative rights that you grant to users in your farm apply to all servers in the farm. It is not possible to grant users administrative rights on some servers while preventing them from administering others in the farm. If you need to segment the administration of MetaFrame XP servers, then you need to create multiple server farms.
Feature Release 2 for MetaFrame XP does introduce the concept of segmented administration. However, this administration is segmented by role, not by server. What this means is that if you have a large farm, you can give some users administrative rights over certain roles, such as printer management or application management, while preventing them from having the ability to change the network configuration of servers or add new servers to the farm. The problem with this is that these rights also apply to all servers in the farm. Users who are only granted the right to manage printers have that right on all farm servers. There is still no way to let some users administer certain servers while preventing them from administering other servers in the same farm.
MetaFrame XP servers in server farms need to communicate with each other. For this communication, consistent network connectivity is needed. If you have any network connections that are extremely limited or unreliable, you may not want to span one farm across them, choosing instead to create two farms, one on each side.
MetaFrame XP licensing is connection-based, which means that one user can simultaneously run sessions on multiple MetaFrame XP servers in the same farm and only use one license. However, if one user connects to servers in two different server farms, one license is required for each server farm. If you want users to only use one license, you must put all of the MetaFrame XP servers they use in the same server farm.
Windows Domain / Active Directory Design
The design of your underlying Windows NT domain or Active Directory can also impact your MetaFrame XP server farm design. There is no problem with having multiple MetaFrame XP server farms in one Windows domain. However, the opposite is not necessarily true. Ideally, a farm should not span multiple NT domains or Active Directory forests. While there is no technical reason that one server farm could not span multiple domains; management becomes much more complex. (Refer to Chapter 17 for more details.)
When designing server farm boundaries, you need to think about the locations of your MetaFrame XP servers in addition to the locations of the users that will be accessing the servers. For example, if you have decided that you need to have multiple groups of MetaFrame XP servers in different geographic areas, but users from each area only connect to their local MetaFrame XP servers, then you can easily make the decision to create multiple server farms.