Logical partition overview

Logical partitioning is the ability to make a server run as if it were two or more independent servers. When you logically partition a server, you divide the resources on the server into subsets called logical partitions. You can install software on a logical partition, and the logical partition runs as an independent logical server with the resources that you have allocated to the logical partition.

Processors, memory, and input/output devices are examples of resources that you can assign to logical partitions. Examples of the kinds of software that you can install and run on logical partitions include the AIX®, i5/OS®, and Linux® operating systems and Virtual I/O Server software.

Logical partitions share a few system attributes, such as the system serial number, system model, and processor feature code. All other system attributes can vary from one logical partition to another.

You must use tools to partition your servers. The tool that you use to partition each server depends upon the server model and the operating systems and features that you want to use on the server.

Benefits of partitioning

The following scenarios illustrate the benefits of partitioning your server:

Consolidating servers: A logically partitioned server can reduce the number of servers that are needed within an enterprise. You can consolidate several servers into a single logically partitioned system. This eliminates the need for, and expense of, additional equipment.
Sharing resources: You can quickly and easily move hardware resources from one logical partition to another as needs change. Features such as Micro-Partitioning™ allow for processor resources to be shared automatically among logical partitions that use the shared processor pool. Other features, such as dynamic logical partitioning, allow for resources to be moved to, from, and between running logical partitions manually without shutting down or restarting the logical partitions.
Maintaining independent servers: Dedicating a portion of the resources (disk storage unit, processors, memory, and I/O devices) to a partition achieves logical isolation of software. If configured correctly, logical partitions also have some hardware fault tolerance. Batch and 5250 on-line transaction processing (OLTP) workloads, which might not run well together on a single machine, can be isolated and run efficiently in separate partitions.
Creating a mixed production and test environment: You can create a combined production and test environment on the same server. The production partition can run your main business applications, and the test partition is used to test software. A failure in a test partition, while not necessarily planned, will not disrupt normal business operations.
Merging production and test environments: Partitioning enables separate partitions to be allocated for production and test servers, 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. As new projects are developed, they can be built and tested on the same hardware on which they will eventually be deployed.
Running integrated clusters: Using high-availability application software, your partitioned server can run as an integrated cluster. You can use an integrated cluster to protect your server from most unscheduled failures within a partition.

Although there are many benefits to using logical partitioning, consider the following points before choosing to partition.

Processor and memory failures might result in the failure of the entire server with all of its logical partitions. (The failure of a single I/O device affects only the logical partition to which the I/O device belongs.) To reduce the possibility of system failure, you can use the Advanced System Management Interface (ASMI) to set the server so that the server can deconfigure failing processors or memory modules automatically. After the server deconfigures the failing processor or memory module, the server continues running without using the deconfigured processor or memory module.
There are many concepts that you must understand to implement logical partitions successfully on your server.
Administering a consolidated system might be more difficult in some ways than administering multiple smaller systems, particularly if the resources in the consolidated system are used at a level close to their capacity. If you anticipate that you will use your server at a level close to its capacity, consider ordering a server model that is capable of Capacity on Demand (CoD).

Sharing resources

Although each logical partition acts as an independent server, the logical partitions on a server can share some kinds of resources with each other. The ability to share resources among many logical partitions allows you to increase resource utilization on the server and to move the server resources to where they are needed. The following list illustrates some of the ways in which logical partitions can share resources. For some server models, the features mentioned in this list are options for which you must obtain and enter an activation code.

Micro-Partitioning (or shared processing) allows logical partitions to share the processors in the shared processor pool. The shared processor pool includes all processors on the server that are not dedicated to specific logical partitions. Each logical partition that uses the shared processor pool is assigned a specific amount of processor power from the shared processor pool. If the logical partition needs more processor power than its assigned amount, the logical partition is set by default to use the unused processor power in the shared processor pool. The amount of processor power that the logical partition can use is limited only by the virtual processor settings of the logical partition and the amount of unused processor power available in the shared processor pool. For more information about Micro-Partitioning, see Shared Processors.
Dynamic logical partitioning allows you to move resources to, from, and between running logical partitions manually without shutting down or restarting the logical partitions. This allows you to share devices that logical partitions use occasionally. For example, if the logical partitions on your server use an optical drive occasionally, you can assign a single optical drive to multiple logical partitions as a desired device. The optical drive would belong to only one logical partition at a time, but you can use dynamic logical partitioning to move the optical drive between logical partitions as needed. On servers that are managed using the Integrated Virtualization Manager, dynamic logical partitioning is supported only for the management partition. Dynamic logical partitioning is not supported on servers that are managed using the Virtual Partition Manager.
Virtual I/O allows logical partitions to access and use I/O resources on other logical partitions. For example, virtual Ethernet allows you to create a virtual LAN that connects the logical partitions on your server to each other. If one of the logical partitions on the server has a physical Ethernet adapter that is connected to an external network, you can configure the operating system of that logical partition to connect the virtual LAN with the physical Ethernet adapter. This allows the logical partitions on the server to share a physical Ethernet connection to an external network.
A Host Ethernet Adapter (HEA) allows multiple logical partitions to share a single physical Ethernet adapter. Unlike most other types of I/O devices, you can never assign the HEA itself to a logical partition. Instead, multiple logical partitions can connect directly to the HEA and use the HEA resources. This allows these logical partitions to access external networks through the HEA without having to go through an Ethernet bridge on another logical partition.

Supported operating systems and software

The operating systems and software that are supported on IBM® eServer™ hardware varies by server line.

The following table details the operating systems and software that is supported on each server line.

Table 1. Supported operating systems and software for logical partitions on IBM Systems and eServer environments
	IBM eServer i5	IBM System p5® and eServer p5	IBM eServer OpenPower®
AIX	Yes	Yes	No
i5/OS	Yes	Yes	No
Linux	Yes	Yes	Yes
Virtual I/O Server	Yes	Yes	Yes
Windows® environment integrated on iSeries®	Yes	Yes	No
Linux environment integrated on iSeries	Yes	Yes	No

Managed Systems

A managed system is a single physical server and the resources that are connected to the physical server and managed by the physical server as a single unit. Connected resources can include expansion units, towers, and drawers, and storage area network (SAN) resources that are assigned to the server.

You can install a single operating system on a managed system and use the managed system as a single server. Alternately, you can use a partitioning tool, such as the Hardware Management Console (HMC), to create multiple logical partitions on the managed system. The partitioning tool manages the logical partitions on the managed system.

The HMC can manage more than one managed system.

In this figure, you can see the logical partitions on each managed system, with the operating systems installed on the disk drives of the physical server and the connected expansion units. The HMC is connected to both managed systems simultaneously and allows you to manage both managed systems from a single location.