Often when installing software for a customer, the customer wants it installed quickly so they can use it immediately. I’ve seen to many rushed installs that lead to many different problems, one of which is not being sized correctly. Before installing any Oracle product, it is always a good idea to consult the Oracle documentation about recommended requirements for the product being installed. In the case of Oracle Enterprise Manger (OEM) 12c, there are size requirements that should be followed for best practices.
There are two types of size requirements: Oracle Management Server (OMS) and Management Repository (database). The size requirement for OMS and Management Repository can be found in the Oracle documentation under chapter 3 of the basic installation guide.
Notice that the hardware requirements are different depending on the size of your environment. The size of your environment is driven by the number of targets and the number of concurrent users connected to the environment. Remember, targets are anything that OEM monitors. In keeping with best practices, it is good to go with mid-size environment, unless already identified. This will give you plenty of performance if you are a small environment and help you identify if you need to go bigger if you are a large environment . The images below will help you determine what requirements and sizes are needed for an environment before installing OEM12c.
CPU, RAM, Heap Size, and Hard Disk Space Requirements for OMS:
CPU, RAM, and Hard Disk Space Requirements for Management Repository:
Now that we have identified two different set of requirements. What if we want to put the OMS and the repository on the same host, as many organizations do. The answer is simple, we need to sum the CPU, RAM and the Hard Disk space together and use those values to build the environment.
By sizing the Oracle Enterprise Manager environment correctly, the scalability and performance of OEM can be easily handled and will yield a positive experience for who ever uses it.