Workload Partitioning (WPAR) in AIX 6.1

WPARs are a bold new innovation, implemented within AIX 6.1. It allows administrators to virtualize their operating system, which allows for fewer operating system images on your IBM System p™ partitioned server. Prior to WPARs, you would need to create a new Logical Partition (LPAR) for each new "isolated" environment. This is no longer necessary (with AIX 6.1 only), as there are many circumstances when one can get along fine with multiple WPARs within one LPAR. Why is this important? Every LPAR requires its own operating system image and a certain number of physical resources. While you can virtualize many of these resources, there are still some physical resources that must be allocated to the system. 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).
WPARs are much simpler to manage and can actually be created from the AIX command line or through SMIT. LPARs cannot. By far the biggest disadvantage of LPARs is maintaining multiple images, which goes along with possibly over-committing expensive hardware resources, such as CPU and RAM. In other words, while 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. It does this by sharing OS 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, which is an important side-benefit. On the other side of the coin, it's important to understands 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, for that matter), all underlying WPARs will also be affected.

Workload Partitions (WPARs) are virtualized operating system environments that are created within a single AIX (only supported on AIX 6.1) image. While they may be self-contained in the sense that each WPAR has its own private execution environment with its own filesystems and network addresses, they still run inside the global environment. The global environment -- the actual LPAR -- owns all the physical resources of the logical partition. It is important to also note that the global environment can see all the processes running inside the specific WPARs.
There are two types of WPARs: system workload partitions and application workload partitions. The system WPAR is much closer to a complete version of AIX. The system WPAR has its own dedicated, completely writable filesystems along with its own inetd and cron. Application WPARs are real, lightweight versions of virtualized OS environments. They are extremely limited and can only run application processes, not system daemons such as inetd or cron. One cannot even define remote access to this environment. These are only temporarily objects; they actually disintegrate when the final process of the application partition ends, and as such, are more geared to execute processes than entire applications. Overall, 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.

via [ IBM ]