Additionally, licensing will need to be maintained for each server that will connect. A direct connection requires each Presentation Server to maintain its own connection to the data store therefore, it will require all the necessary database client software (such as the MDAC, Oracle client, or DB2). Thus, most architects agree that a direct connection method is the best in terms of scalability and fault tolerance. As you can see, Server1 is the single point of failure and a major scalability concern. If Server2, a member of the same farm, needs to gain access to the farm database, the IMA service on Server2 communicates with the IMA service on Server1, and then the IMA service on Server1 fulfills the request for Server2 and returns the results via IMA (thus indirectly). In other words, if Server1 were the first server in the farm, it would maintain the MS Access database. Why, you may ask? Since the database exists on the first Citrix server in the farm, all servers must communicate indirectly via the IMA service to gain information from the database. Indirect connections are required for servers that are members of the farm where a local data store database (MS Access or MSDE) is used. Depending on the type of data store database you select, you will have options here. Good for larger farms (five servers and larger)ĭata store connections come in two flavors, direct and indirect. More fault tolerant through database clustering ▪ More scalable through database replication ▪ More flexible, as the database is separate from a Presentation Server in the farm ▪ Let's outline some of the facts and best practices around these two types to allow us to make the best design decisions for our environment.Īdditional cost for database server and licenses ▪ Each type, local or network, has its benefits and disadvantages. The network data store databases can leverage MS SQL, Oracle, or IBM's DB2. The local data store databases consist of two formats, either MS Access or Microsoft SQL Desktop Engine (MSDE). At the time of creation of a new farm, the “type” of database must be considered, as it will impact the design, scalability, and cost of the server farm. There are two types of data store databases: local databases and network databases. The servers that are members of the given farm, which this specific data store defines, perform read/write operations against this data store database based on the configuration we enter as administrators into the Presentation Server Management Console and the server-to-server communication associated with the Independent Management Architecture service. The data store is a standard database format. The data store retains information that does not change frequently, including the following: ▪ The data store provides a repository of persistent farm information for all servers to reference. Read moreĪll XenApp servers within a farm all share a common repository for configuration known as the data store. By default, XenApp server maintains this database in the path C:\Program Files\Citrix\Independent Management Architecture in a file named MF20.MDB. This provides much greater scalability and much less reliance on the server housing the data store database. Therefore, with a partial replica being available locally, the IMA service can review those settings and synchronize in the background with the “master” copy of the data store. In a larger farm, this could lead to a bottleneck at the server housing the database. Servers may need to frequently consult the information in the data store database. The second reason is all about performance. Therefore, in the event of failure of the server that houses the actual data store, the farm could continue functioning for up to 96 hours (based on a hard limit imposed by Citrix). First, by maintaining a local partial replica of the data store database, the XenApp server could continue running based on the configuration that is last received from the data store. There are many reasons why a XenApp server would want to maintain a partial copy of the data store database locally however, two reasons sum up most of the logic behind this decision. The partial local replica is maintained in MS Access format and is encrypted, similar to the information in the data store database. The LHC is a partial copy of the data store database that every XenApp server maintains locally to the server itself (hence the name). The next component to consider is the local host cache (LHC). Tariq Bin Azad, in Securing Citrix Presentation Server in the Enterprise, 2008 Local Host Cache Terminal Services and XenApp Server Deployment
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