 | Level: Intermediate Jack Alford (alfordja@us.ibm.com), Advisory Human Factors Engineer, IBM
20 Nov 2007 Workload Partitions (WPARs) are a new virtualization feature of
AIX® 6.1. This article helps you decide whether WPARs are right for your AIX
workloads, and then gives you step-by-step guidance on how to learn more about WPARs
and begin using them.
Getting started with
Workload Partitions in AIX 6.1
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.
Using WPARs
Are you ready to create your first workload partition? All you need to get
started is the capability to log in as the root user on an AIX 6
system—the official 6.1 product version is the most up-to-date but, if you
happen to have downloaded an early copy during the Open Beta program, you can use
that for basic WPAR operations.
Define a WPAR
Log in as root on your AIX 6 system, and run the following command:
That is all you need to do to create a system WPAR whose name is mywpar.
After pressing the Enter key, a long series of messages display on the
console that look very similar to those you see during a typical AIX installation.
After a few minutes, a message displays, followed by a command prompt indicating
that the WPAR creation is complete. To verify that your WPAR was created, run the
following command to list all defined WPARs:
Listing 1 displays a table showing the WPAR named
mywpar that you just created. The D in the State field means
the WPAR is Defined; it exists, but it has not been started. It has a type
of S
—that is, it’s a system WPAR, because the
mkwpar command creates system WPARs by default. Also by
default, the hostname is the same as the WPAR name, and the base directory for all
the WPAR’s filesets is located at /wpars/<wpar name>.
Listing 1.
lswpar command output
# lswpar
Name State Type Hostname Directory
---------------------------------------------
mywpar D S mywpar /wpars/mywpar
#
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To start your new WPAR and log in, run the following command:
Running the lswpar command again indicates that state
of the WPAR changed from D to A (for Active).
You have not defined network information for this WPAR, so unless the name you
picked for your WPAR already resolves to a valid network address, you probably
won’t be able to do any kind of network login yet. Since you are still on the
system console, do a console login to the new WPAR:
The AIX welcome message and command prompt displays. You have created, started,
and logged in to your first WPAR! Run the hostname
command to confirm this.
From this point, you can run most AIX commands, define other users, and do most
anything you would do with a full AIX system.
Once you have logged into the WPAR, there is one important point to remember:
From the WPAR, you have no access to the global system or to any other WPAR. So
some familiar commands or SMIT menus will not work as they usually do, or they
might be missing altogether. For example, if you enter the
hostname command, it returns the name of the WPAR and
not the hostname of the global AIX system. So for now, let’s leave the WPAR, and
return to the global AIX environment by typing the exit
command. Then to stop the WPAR, just type:
Using SMIT to change WPAR
properties
How about using SMIT to define an IP address for the new WPAR? Of course, you can
also do this using the command line, since SMIT is just a command processor. On
the global AIX command line, type smit to display the
initial SMIT menu. You’ll see a new menu choice, Workload Partition
Administration.
After selecting Workload Partition Administration, you’ll see three choices:
List All Workload Partitions
Administer SYSTEM Workload Partitions
Administer APPLICATION Workload Partitions
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The first choice, List All Workload Partitions, executes the
lswpar command to show all defined WPARs on your
system. Choose Administer SYSTEM Workload Partitions to work with the WPAR
you defined earlier. This selection displays the following sub-menu:
List System Workload Partitions
Create a System Workload Partition or Specification File
Start / Stop / Reboot a System Workload Partition
System Workload Partition Software Maintenance
Change / Show System Workload Partition Characteristics
Remove a System Workload Partition
System Workload Partition Backup Manager
|
You do not need to create a WPAR, so select Change / Show System Workload
Partition Characteristics, which results in the following submenu:
Change / Show General Characteristics
Change / Show Network Interfaces
Change / Show File Systems
|
The first choice, Change / Show General Characteristics, displays an input
panel that lets you view or change the basic WPAR properties, such as the WPAR
name, hostname, start options, and more advanced settings, including resource
controls and security settings. You set out to work with network settings, so
select Change / Show Network Interfaces, which results in the following
data entry fields:
[Entry Fields]
* Workload Partition Name []
+ Network INTERFACE
+
* Internet ADDRESS (dotted decimal) []
Network MASK []
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- Type or select the WPAR name in the Workload Partition Name field.
- In the Network INTERFACE field press F4 or Esc+4 to show
the list of available network interfaces. Select the one that you want to use,
then enter a valid IP address and network mask in the remaining fields
If you plan to define a bunch of WPARs, you’ll need to secure in advance a group
of available hostnames and IP addresses in your network.
After completing the panel for adding a network interface, you can start the
WPAR, either by using SMIT menus, or issuing the
startwpar command from the command line. After the WPAR
has started, you should be able to log in remotely using telnet. Don’t forget to
set a root password and any other security measures that you normally take when
setting up a new AIX system. You might also want to add a line to the /etc/hosts
file on the global system containing the hostname and IP address of the new WPAR.
Now that you can log in to your new system WPAR, either from the system console
or remotely, you can do many of the things you would do with any new AIX system:
create users, create new file systems, or install software. Regarding software
installation, you might use NIM to perform network installs. Or, you can add a
CD-ROM file system to the WPAR, which enables you to use a CD-ROM attached to the
physical server to install software on the WPAR.
Creating and using
application WPARs
Creating an application WPAR is similar to creating a system WPAR. However,
instead of the mkwpar command, you use the
wparexec command, which not only creates the WPAR, but
it also starts the application inside it. As previously noted, an application WPAR
only exists so long as the application process is running. Once the process
terminates, the WPAR is stopped and cleaned up.
To create an (somewhat trivial) application WPAR named mywpar that will
sleep for 100 seconds, enter the command:
wparexec –n myappwpar /usr/bin/sleep 100 &
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After pressing Enter, several messages display indicating that the WPAR is
starting and that file systems are being mounted. If you type the
lswpar command, the following displays:
# lswpar
Name State Type Hostname Directory
---------------------------------------------
myappwpar A A myappwpar /
#
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This information indicates that a WPAR named myappwpar exists, that it is in an
active state, and that it is an Application WPAR. After 100 seconds, a message
displays that the system is shutting down all WPAR processes. Enter
lswpar again to verify that the WPAR no longer exists.
WPAR Manager
IBM Workload Partitions Manager for AIX (WPAR Manager) is a platform management
solution that provides a centralized point of control for managing workload
partitions across a collection of managed systems running AIX 6.1. The managed
systems might all be LPARs on a single physical server, or they might be located
on multiple physical servers. Using WPAR Manager, you can monitor the health and
status of multiple WPARs on multiple managed AIX systems. You can also perform all
the basic WPAR life cycle operations—including create, view and manage
properties, start, stop, and delete.
WPAR Manager also supports relocation of WPARs between systems in a collection of
managed servers. WPAR Manager supports two kinds of relocation:
- Manual relocation—This type of relocation is initiated by the user.
- Policy-based relocation—This type of relocation is initiated by WPAR
Manager in response to workload conditions defined in a relocation policy.
WPAR Manager is not part of AIX—it’s a separately purchased licensed
program (Program number 5756-WPM). But, if you are working with an AIX 6 image
that you downloaded during the Open Beta program, you might have the early version
of WPAR Manager that was shipped with the beta. This article only touches on the
main capabilities of WPAR Manager. A later article will present a more detailed
description of how it works and how to use it.
Multi-system management
Managing WPARs on multiple AIX systems using the WPAR Manager requires two
initial installation and configuration steps. First, you install and configure the
management server software on an AIX system in your environment. Then, you install
the WPAR Manager agent software on each AIX system that will be managed by WPAR
Manager. The agent must then be configured to share WPAR data with a specific
management server. After the WPAR Manager and agent components have been
configured and started, the WPAR Manager automatically discovers all the managed
systems, and begins to record data transmitted by the agents in an internal
database.
One of WPAR Manager’s main resource views shows all managed AIX
systems—that is, all AIX systems on which the WPAR Manager’s agent
software has been installed and configured to communicate with the WPAR Manager
server. This view provides information about the characteristics of each managed
system, including its current operational state and connectivity with the WPAR
Manager. From this view, you are able to drill down to see all the WPARs defined
on any of your managed systems. You can also create and delete WPARs and perform
any other life cycle tasks.
Figure 1. WPAR
Manager systems view
Another main resource view shows all defined WPARs in your management
environment. The WPARs in the list can be in one of several states:
- Active on one of the managed systems.
- Deployed on a managed system, but not currently running.
- Undeployed, that is, defined in the WPAR Manager’s database, but not yet
deployed to any managed system.
There are also several other transitional and error states.
Figure 2. WPAR
Manager WPARs view
In addition to the main resource views and associated task panels, the WPAR
Manager contains both wizard and power user interfaces for creating WPARs
and WPAR groups and for relocating WPARs from one system to another. There are
also panels for viewing the status of tasks that you have initiated and for
monitoring the performance of WPARs over time.
Live Application Mobility
Live Application Mobility is the capability to relocate a WPAR from one hosting
system to another without having to restart any applications or processes running
in the WPAR. (Live Application Mobility is the term seen in marketing materials,
while the WPAR Manager’s user interface uses relocation.) It is important
not to confuse Live Application Mobility with another recently announced feature
of POWER6 servers: Live Partition Mobility. Partition mobility refers to the
ability to move an entire running AIX LPAR from one physical server to another.
Being a hardware-based function, partition mobility is only supported on POWER6
hardware; application mobility is supported on any hardware that supports AIX 6.
When a WPAR is relocated using WPAR Manager, all processes are checkpointed and
then restarted on the target system, with minimal impact on the application or
WPAR user. Although it is possible to use AIX commands to checkpoint a WPAR, copy
critical files to another system, and then restart the WPAR on the target system,
it is not easy, and the relocation might fail due to user error. Another important
reason to use WPAR Manager to relocate WPARs is that it also offers an automated
recovery mechanism. If, for whatever reason, the relocation process goes bad, WPAR
Manager can be successful in restoring the WPAR to its original location and
state. Log files and task status displays in the graphical user interface let you
know if a task failed and provide stderr output to help understand what went
wrong.
Policy-based relocation
WPAR Manager also has the capability to monitor performance of workloads running
in WPARs and relocate those workloads to different AIX systems to improve
performance. For example, if CPU or memory usage in a WPAR or group of WPARs is,
on average, higher than a value that you specify, then the WPAR Manager might
attempt to relocate one or more WPARs to a more powerful, or less busy, server in
your datacenter. The detailed mechanics of how the policy engine works are beyond
the scope of this article, but will be covered in a later article.
WPAR Manager Information
Center
The WPAR Manager Information Center is available from any panel in WPAR Manager
by clicking on the Help link at the top of the WPAR Manager browser window.
The same material is available in the AIX Information Center—look under
the "IBM Workload Partitions Manager for AIX" heading (see
Resources).
You can access help for individual pages by clicking the question mark icon at
the upper right of any active WPAR Manager page. The page help provides detailed
information on how to interact with the page being viewed.
Conclusion
In this article, you learned the following basics of workload partitions in AIX
6.1:
- WPARs are software-based partitions that extend and complement the System p
server’s hardware-based LPARs.
- There are two types of WPARs: System and Application. Which is best for
you depends on your requirements for workload isolation, mobility, and how
complete an operating environment you need.
- You can create a WPAR quickly using either AIX commands or SMIT.
- Other commands and SMIT menus let you modify, start, stop, or remove WPARs.
- The WPAR Manager, a separate licensed program, extends WPAR management to
multiple systems, and supports relocation of WPARs from one system to
another.
The information presented here should encourage you to try out WPARs in your AIX
6.1 environment, and see for yourself what this new virtualization capability can
do for you.
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About the author | | | Jack Alford has been a human factors engineer at IBM for 27 years, designing and testing user interfaces for system management tools for the VM and AIX operating systems, including the IBM Workload Partitions Manager for AIX. You can contact him at alfordja@us.ibm.com. |
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