Common Service Layer overview

The IMS Common Service Layer (CSL) is a collection of IMS manager address spaces that provide the infrastructure needed for systems management tasks in an IMSplex. The CSL address spaces include Open Database Manager (ODBM), Operations Manager (OM), Resource Manager (RM), and Structured Call Interface (SCI).

The CSL is built on the IMS Base Primitive Environment (BPE) layer. As a result, all BPE externals, such as commands, messages, abends, configurations, and user exit interfaces apply to all CSL manager address spaces.

The IMS CSL provides:

  • Improved systems management
  • A single system image
  • Ease of use through a single point of control
  • Shared resources across all IMS systems

A single CSL can service multiple IMS systems within an IMSplex, either on the same operating system or on multiple operating systems.

Recommendation: Activate more than one CSL manager of each type in the IMSplex. An IMS control region within an IMSplex that is defined with CSL cannot start unless at least one OM is active in the IMSplex and an SCI resides on every operating system in the IMSplex. This recommendation also applies to RM, although an RM is not required for an IMS control region to start.

There are advantages and disadvantages of having all CSL managers on each operating system. One advantage is better system performance. It is faster for an IMSplex member to communicate with a CSL manager on the same operating system than it is for the IMSplex member to communicate with a CSL manager on a different operating system. A disadvantage is the increased number of address spaces on each operating system. However, if only one instance of a CSL manager is defined in an IMSplex, whether it is ODBM, OM, or RM, no backup of that CSL manager exists if it should fail.

If you do not use shared queues or sysplex technology, you can take advantage of a simplified CSL configuration to issue type-2 commands through the CSL OM.