Zone Data Collector ( ZDC)

Citrix Zone Data Collector

A data collector is a server that hosts an in-memory database that maintains dynamic information about the servers in the zone, such as server loads, session status, published applications; users connected, and license usage. Data collectors receive incremental data updates and queries from servers within the zone. Data collectors relay information to all other data collectors in the farm. By default, the first server in the farm functions as the data collector.
By default, the data collector is configured on the first farm server when you create the farm and all other servers are configured with equal rights to become the data collector if the data collector fails. When the zone’s data collector fails, a data collector election occurs and another server takes over the data collector functionality. Farms determine the data collector based on the election preferences set for a server.

Data collectors receive incremental data updates and queries from servers within their zone. Data collectors relay information to all other data collectors in the farm. The data collector tracks, for example, which applications are available and how many sessions are running on each server in the zone. The data collector communicates this information to the data store on behalf of the other servers in the farm. By default, in farms that communicate indirectly with the data store, the first server in the farm functions as the data collector.

Data collector is a role on a Citrix XenApp server which is collecting, maintaining and managing dynamic information about the farm and zone. The data collector also passes the user to the least busy server.

Data Collector contains dynamic information about the servers in a zone, including:-

    Published Applications usage,
    Server load,
    User sessions,
    Online servers,
    Connected sessions,
    Disconnected sessions, and
    Load balancing information.

If the data collector fails, existing and incoming sessions connected to other servers in the farm are not affected. The data collector election process begins automatically and a new data collector is elected almost instantaneously. Data collector elections are not dependent on the data store.

New Data Collector Election

When communications fail between data collectors or between a server and its data collector, the process to choose or elect a new data collector begins. For example:

1. The data collector for Zone 1 has an unplanned failure. If the data collector shuts down correctly, it triggers the election process as it shuts down.
2. The servers in Zone 1 detect the data collector failed and start the election process. The server set to the next highest election preference is elected as the new data collector.
3. The member servers start sending their information to the new data collector for Zone 1.
4. The new Zone 1 data collector replicates this information to the other data collectors in the farm.

Planning for Data Collector-

In general, data collector memory consumption increases as farm size increases. However, it is not significant. For example, the Independent Management Architecture service running on the data collector typically uses 300 MB on a 1000 server farm.
Likewise, CPU usage is not significant. A data collector hosted on a dual-processor server can support over 1000 servers in its zone. In general, CPU usage increases as the number of servers in a zone increases, the number of zones increases, and the number of users launching applications increases.
On most networks, Citrix recommends reducing the number of data collectors and zones. For example, if you have a farm with 100 servers in one location, Citrix recommends having one zone with a dedicated data collector (although you can have backup data collectors).
Citrix recommends installing XenApp on the server you want to host the data collector functionality and, after installing other member servers, configuring a server as the backup data collector.