Partitioning your system is similar to partitioning a hard drive. When you partition a hard drive, you divide a single physical hard drive so that the operating system recognizes it as a number of separate logical hard drives. You have the option of dividing the system's resources by using the Hardware Management Console (HMC) to partition your system. On each of these divisions, called partitions, you can install an operating system and use each partition as you would a separate physical system.
A managed system is a system that is physically attached to and managed by the HMC. The HMC can perform tasks that affect the entire managed system, such as powering the system on and off. You can also create partitions and partition profiles within each managed system. These partitions and partition profiles define the way that you configure and operate your partitioned system.
A logical partition (LPAR) is the division of a computer's processors, memory, and hardware resources into multiple environments so that each environment can be operated independently with its own operating system and applications. The number of logical partitions that can be created depends on the system's processor model and resources available. Typically, partitions are used for different purposes, such as database operation, client/server operations, Web server operations, test environments, and production environments. Each partition can communicate with the other partitions as if each partition is a separate machine.
Beginning with AIX 5.1, the AIX operating system supports partitioned environments. Although the AIX installation concepts are the same, the ability to configure and manage a partitioned environment with the AIX operating system is available in AIX 5.2. This guide assumes the reader has some familiarity with partition management. For more information about partition management, refer to the IBM Hardware Management Console for pSeries Installation and Operations Guide, order number SA38-0590.
A logical partition must contain a minimum set of resources, as follows:
Processors, memory, and I/O slots can be allocated to any partition, regardless of their location. However, if you attempt to activate a partition, but the resources you specified are not available at the time, partition activation fails. It is important to keep track of your system's resources to avoid activation failures. PCI slots are assigned individually to partitions, and memory can be allocated in 256 MB increments. The granularity of the resources that can be assigned to partitions is very fine, providing flexibility to create systems with just the desired amount of resources. Each partition runs its own copy of the AIX operating system and is isolated from any activity in other partitions. Software failures do not propagate through the system, and the hardware facilities and microcode isolate the resources.
Dynamic logical partitioning provides the ability to logically attach and detach a managed system's resources to and from a logical partition's operating system without rebooting.
For more information on dynamic logical partitioning, see the following:
Some systems have the ability to create affinity logical partitions. Check your hardware specifications to see if your managed system is capable of using affinity logical partitions. An affinity logical partition is a special type of logical partition that uses system resources that are in close physical proximity to each other. When creating an affinity logical partition, the HMC automatically determines which system resources are to be used, based on their physical location to each other. The system resources that are automatically managed by the HMC are processors and memory. The user determines the I/O requirements for each of these partitions. The HMC then creates a profile for each affinity logical partition and a system profile for the managed system.
The logical partition resource allocation provides the ability to select individual components to be added to a partition without dependencies between these resources. The slots can be freely allocated in any I/O drawer on the system. Other devices may be required for specific application requirements. It is a good idea to configure more PCI slots in the partition than are required for the number of adapters. This provides flexibility by allowing additional adapters to be hot-plugged into the empty slots that are part of an active partition. Because each partition requires its own separate boot device, the system must have at least one boot device and associated adapter per partition.
There are a few differences in how AIX runs within a logical partition, as opposed to how it runs on a standalone server:
Apart from these considerations, AIX runs within a partition the same way it runs on a standalone server. No differences are observed either from the application or the administrator's point of view. Third-party applications need only be certified for a level of AIX that runs in a partition, and not for the LPAR environment itself.
A special partition called the Full System Partition assigns all of your managed system's resources to one large partition. The Full System Partition is similar to the traditional, non-partitioned method of operating a system. Because all resources are assigned to this partition, no other partitions can be started when the Full System Partition is running. Likewise, the Full System Partition cannot be started while other partitions are running. It is recommended that you choose to use either the Full System Partition or create other partitions. It is not recommended that you switch between these two options frequently, because your I/O usage might be affected.
Use the following illustration to help you locate information about understanding, planning for, and configuring partitions, as well as information about installing the AIX operating system.
A logically partitioned environment adds to a portfolio of solutions that can provide better management, improved availability, and more efficient use of resources. This section provides some scenarios where a logically partitioned environment brings significant benefits, as well as other scenarios where it may not be appropriate.
A server with sufficient processing capacity that is capable of being partitioned can address the need for server consolidation by logically subdividing the server into a number of separate smaller systems. In this way the application-isolation needs can be met in a consolidated environment, with the additional benefits of reduced floor space, a single point of management, and easier redistribution of resources as workloads change.
Generally, production and test environments should be isolated from each other. Partitioning enables separate partitions to be allocated for the production and test systems, eliminating the need to purchase additional hardware and software. When testing has been completed, the resources allocated to the test partition can be returned to the production partition or elsewhere as required. It might be that the test environment later becomes the production environment, and extra resources can then be added to the partition. As new projects are developed, they can be built and tested on the same hardware on which they will eventually be deployed.
Starting with AIX 5.1, different versions of AIX can exist within different LPARs in the same system. This enables a single system to have different versions of the operating system installed to accommodate multiple application requirements. Furthermore, an LPAR can be created to test applications under new versions of the operating system prior to upgrading the production environments. Instead of having a separate server for this function, a minimum set of resources can be temporarily used to create a new LPAR where the tests are performed. When the partition is no longer needed, its resources can be incorporated back into the other LPARs.
