IBM Workload Partitions (WPARs) are implemented starting with AIX 6.1. Workload Partitions allow administrators to virtualize the AIX operating system, by partitioning an AIX operating system instance into multiple environments. Each environment within the AIX operating system instance is called a workload partition (WPAR). One WPAR can host applications and isolate the applications from applications executing in other WPARs. WPAR is a pure software solution and has no dependencies on hardware features.

The WPAR solution allows for fewer operating system images on your IBM System p partitioned server. Prior to WPARs, you had to create a new Logical Partition (LPAR) for each new "isolated" environment. Starting with AIX 6.1, you can instead use multiple WPARs within one LPAR, in many circumstances.

In an LPAR environment, each LPAR requires its own operating system image and a certain number of physical resources. While you can virtualize many of these resources, some physical resources must be allocated to the system for each LPAR. Furthermore, you need to install patches and technology upgrades to each LPAR. Each LPAR requires its own archiving strategy and DR strategy. It also takes some time to create an LPAR; you also need to do this outside of AIX, through a Hardware Management Console (HMC) or the Integrated Virtualization Manager (IVM).

In contrast, WPARs are much simpler to manage and can be created from the AIX command line or through SMIT. WPARs allow you to avoid the biggest disadvantage of LPARs: maintaining multiple images, and therefore possibly over-committing expensive hardware resources, such as CPU and RAM. While logical partitioning helps you consolidate and virtualize hardware within a single box, operating system virtualization through WPAR technology goes one step further and allows for an even more granular approach of resource management.

The WPAR solution shares operating system images and is clearly the most efficient use of CPU, RAM, and I/O resources. Rather than a replacement for LPARs, WPARs are a complement to them and allow one to further virtualize application workloads through operating system virtualization. WPARs allow for new applications to be deployed much more quickly.

WPARs have no real dependency on hardware and can even be used on POWER4 systems that do not support IBM's PowerVM (formerly known as APV). For AIX administrators, the huge advantage of WPARs is the flexibility of creating new environments without having to create and manage new AIX partitions.

On the other hand, it's important to understand the limitations of WPARs. For example, each LPAR is a single point of failure for all WPARs that are created within the LPAR. In the event of an LPAR problem (or a scheduled system outage), all underlying WPARs are also affected.

The following sections describe the types of WPARs: