AIX 6.1 Workload Partitions – ask us how…
If you are a systems administrator who is responsible for care and feeding of IBM® System p™ servers, you are probably familiar with virtualization and server consolidation using logical partitions (LPARs). Using the Hardware Management Console (HMC) or the Integrated Virtualization Manager (IVM), you can quickly define a new LPAR, install AIX® or Linux®, configure your operating system, install applications, and then put your new virtual server to work.
AIX 6.1 introduces a new mechanism for virtualization: Workload Partitions (WPARs). In this article, you’ll learn the basics of what WPARs are, how they differ from LPARs, and how you can quickly and easily try them out on your AIX 6.1 system. This article also provides some basic rules of thumb to help you decide which virtualization method is most appropriate for you and walks you through the steps to create your first WPAR. Then, you’ll examine additional life cycle management tasks that you can perform from the AIX command line or System Management Interface Tool (SMIT). Because this article is intended to be only a high-level introduction, you’ll find some links to information that help you learn all the technical details about this new technology. Finally, you’ll review some more advanced WPAR features, including Live Application Mobility—the ability to move a running WPAR-based application from one AIX system to another—using a new management tool, the IBM Workload Partitions Manager for AIX (WPAR Manager).
What are WPARs?
In contrast to LPARs, which are created and managed at the server’s firmware level, AIX WPARs are software partitions that are created from, and share the resources of, a single instance of the AIX operating system. This means that you must have AIX 6.1 to create WPARs, but you can create WPARs on any System p hardware that supports AIX 6.1, including POWER4, POWER5, and POWER6 hardware. You don’t need an HMC or IVM to create or manage WPARs.
There are two kinds of WPARs:
* System WPARs
* Application WPARs
System WPARs
System WPARs are autonomous virtual system environments that have their own private file systems, users and groups, login, network space, and administrative domain. To users and applications, a system WPAR appears almost exactly like a full AIX system. Operating system services, such as telnet, are supported, so if network information has been configured, users can telnet into a system WPAR as root or any other defined user, issue commands, and run applications as they would on any other AIX system.
Here are a couple of quick examples of situations in which system WPARs might be useful:
* If you happen to be an administrator for an AIX system used in a university computer science class, you can create a system WPAR for each student. Students can each be the root user of their own private virtual environment—defining users, installing applications, and programming their class assignments. If a student is persuaded to find out what happens when you type rm –r *, only their WPAR is trashed—catastrophic events in one WPAR can’t harm other WPARs or the global AIX environment. At the end of the semester, you might run a script that deletes and cleans up all the class WPARs.
* If you are setting up an application development or test environment, you can create it in a system WPAR. You don’t have to acquire a dedicated server or LPAR but, if the new environment should have serious problems, any adverse effects will be confined to the WPAR.
Application WPARs
Application WPARs provide an environment for isolation of applications and their resources to enable checkpoint, restart, and relocation at the application level. An application WPAR is essentially a wrapper around a running application or process for the purposes of isolation and mobility. It lacks some of the system services provided by system WPARs—for example, it’s not possible to log in or telnet into an application WPAR. When the application running in an application WPAR terminates, the WPAR also ceases to exist. Application WPARs are most useful when you want to enable Live Application Mobility—that is, when you want to be able to move a running application from one AIX system to another. You might want to relocate applications to avoid downtime resulting from scheduled maintenance or to improve performance by moving an application to a more powerful server.
How do WPARs compare with LPARs?
As noted earlier, you do not need access to the HMC or IVM to create WPARs as you do for LPARs. WPARs are lightweight and quicker to install, because they share many of the file systems and resources of the global AIX system in which they reside. While using an LPAR requires you to install an entire operating system, creation of system WPARs only installs private copies of a few file systems, and application WPARs share even more of the global system’s resources. As a result, a WPAR can be created in just a few minutes without installation media. Ongoing administration and maintenance of WPARs should be simpler—fewer AIX licenses might be required, and you don’t have to install fixes and updates on so many virtual systems. There is a command for synchronizing the filesets of a WPAR with the corresponding filesets on the global system, so you have the choice of propagating AIX fixes to WPARs or continuing to run with the current versions of system files.
While LPARs offer a significantly higher degree of workload isolation, WPARs might provide “good enough” isolation for your particular workloads, especially temporary ones such as development or test environments. Similarly, with LPARs, you can achieve a greater degree of control over the usage of resources—by allocating entire processors or precise fractions of processors to an LPAR, for example. With WPARs, you don’t have such fine control over resource allocations, but you can allocate target shares or percentages of CPU utilization to a WPAR (if have used the AIX Workload Manager, you will find the share and percentage resource allocation scheme familiar). Similar differences exist for the allocation of memory, number of processes, and other resources.
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