In an OAM Parallel Sysplex environment, cross-coupling facility (XCF) message services send requests and data between instances of OAM within an OAMplex. XCF messaging services, a function within XCF, uses transport classes to send XCF messages and data through the coupling facility between the various systems within a sysplex environment.

Transport classes are used by XCF messages service to group messages that are to be sent between systems within a Parallel Sysplex. Messages are assigned to transport classes based on the group name (defining specific transport classes to OAM, for example), the message size, or both. Each transport class has its own resources that consist of buffers and one or more inbound and outbound paths. In most cases, it is more efficient to pool the resources and have the transport classes based on message size, rather than on group name.

XCF message buffers are managed by correctly selecting the size of the messages most frequently sent from specific buffer pools and by specifying an adequate upper limit for the size of the buffer pool. Multiple default transport classes of various sizes are assigned to the multiple buffers in the coupling facility. XCF determines which transport class is to be used depending on the size of the message or object in the buffer being transported.

XCF attempts to optimize the use of transport classes by selecting a class that is large enough to handle all the data being transported. For example, if a message or data is being sent from one instance of OAM to another OAM system within an OAMplex through the coupling facility using XCF message services that is 5 KB in size, XCF might use the 5 KB default transport class to send the message. XCF tries to select the best fit transport class for the buffer size. However, XCF might also choose the 5 KB transport class to handle a 2 KB message if that is the best fit available at the time. The 5 KB default transport would be large enough to handle the request; however, the buffer is not being used efficiently.

It is possible to create customized transport classes based on message size (or object size) to use specifically for your own data by defining transport classes based on message or object size and assigning them based on the OAM XCF group name along with the default transport classes. Defining your own transport classes allows you to determine the best fit for your objects to optimize the use of the transport class for your group class buffer size.

Recommendation: Customizing your own transport classes works best if your installation has standard object sizes. Additionally, you would want to create smaller transport classes for OAM to handle the smaller messages used to communicate configuration updates. In this case, you would have the best fit transport classes for your data and messages.

Perform the following steps to determine if there is a legitimate need for user-defined transport classes:

1. Use the XCF default transport classes assigned to the buffers first to determine if they sufficiently accommodate the size of your data and are being used in an efficient manner.
2. Modify your configuration (storage group, library, and drive definitions) to best utilize your resources and reduce unnecessary XCF messaging for processing transactions. Some libraries span several storage groups, which might increase the need to send messages using XCF. Update your configuration to minimize the frequency and the amount of data that needs to be transported. For OSMC processing, try to run OSMC on the OAM that is managing and controlling the hardware associated with both the Object storage group being processed and the Object Backup storage group. If different storage groups are being processed on multiple OAMs concurrently and backup copies of objects need to be written, you should have hardware available to the Object Backup storage groups on each OAM that is doing the processing.