PowerVM

PowerVM, formerly known as Advanced Power Virtualization, or APV, is the virtualization feature first made available with POWER4 based pSeries computer servers from IBM and enhanced with the later release of POWER5 and POWER6 range of computers. This is an implementation of hardware and software virtualization technology.

The IBM System p and System i family of products share the POWER5 and POWER6 technology platform which is based on the POWER4 hypervisor technology.

In this case, virtualization means one computer running multiple operating systems (and their applications) at the same time. Each operating systems appears to be a separate machine but it is in fact hosted on a single server and sharing resource. When one operating system is not busy then typically its CPU time can be used by one of the others. This can be seen to either boost performance of the busy operating systems (by borrowing resources from unbusy ones) or save money (you buy less computer hardware to run a set of applications).

Description

PowerVM supports Logical Partitions (LPARs) (each LPAR runs a different operating system and its applications). A Logical Partition is defined by the resources assigned to it and can be started and stop independently. A Logical Partition has:
* CPU resources in logical terms from scaling from 1/10th of a CPU up the whole machine. The word logical is used here because you allocate for example three CPUs and not particular physical CPUs as in CPU1, CPU15 and CPU64.
* Logical memory from 256MB to all the memory in the whole machine.
* Physical PCI slots for adapters. For example, network or disk adapters (i.e. SCSI, SAS or SAN adapters).
* Virtual device access to disk space or networks (explained below)

Each logical partition runs its own copy of the operating system (see below for the list) and has a high security rating for example the industry standard CAPP EAL4++ Security Certification for the AIX 5.3 and the Virtual I/O Server. The machines are configured via a Hardware Management Console (HMC) which is a PC style device running special software and connected to the System p machine's embedded Flexible Service Processor (FSP). Systems Administrators access the HMC directly on its keyboard, mouse and screen or remotely via a web browser in the latest release or PC software called WebSM in older releases.

The computers CPU and memory is allocated by size but controlled by the machines hypervisor and it actually decides which CPU or chunk of memory to allocate at LPAR start up time. There are no restrictions and no barriers. For example, there are no special rules such as that particular CPUs must be allocate along with the RAM in certain memory slots. For shared CPU LPARs, the hypervisor dynamically decides which CPU a LPAR will run on next depending on the demand for CPU cycles.

From POWER5 onwards, CPUs are allocated as whole CPUs dedicated to a partitions logical partition or factions of a CPU can be allocated from the shared processor pool. These "micro-partitions" can make use of CPU time allocated to other logical partitions and yield their CPU time if not needed. This means CPU power is moved to the logical partition that needs it with in milliseconds. CPU time is controlled by the following logical partition parameters:
* Entitlement (A guaranteed minimum amount of the resource available)
* Capped or Uncapped (Capping determines whether the LPAR can go over entitlement)
* Virtual processor number (A spreading factor used to control the number of usable physical CPUs)
* Priority weighting (When space CPU capacity is available, this decides which LPAR gets the extra CPU resources) Virtual disks, virtual networks and virtual optical devices are accessed via memory and the hypervisor. The underlying real resources are controls by a logical partition running a special dedicated operating system called the Virtual I/O Server, which is part of the PowerVM package.

Logical partitions can have dedicated hardware resources or virtual resources with no restrictions.

All System p or System i machines use PowerVM. Systems running on POWER5 technology even while configured to run a single operating system still utilize the POWER hypervisor virtualization technology.An example of this is for High Performance Computer (HPC) environment where the user prefers to run a single system image (LPAR) to maximize the available memory and cpu resources, this if often referred to as SMP mode.

On the POWER5 platform even if the system is configured without an Hardware Management Console and is running in single system mode, the hypervisor is still treats that system a single partition.

Editions

PowerVM comes in three versions. All versions have these features:
* Management via browser based Integrated Virtualization Manager (IVM) software
* Lx86, x86 binary translation software, allowing x86 Linux software to run unchanged
* Virtual I/O server, allowing virtualization and partitioning of I/O such as SCSI and Ethernet
* Shared Dedicated Capacity, allowing spare cycles from underutilized dedicated CPU partitions to join the shared CPU pool. On POWER6 systems only.
* Partition load manager, allowing live load balancing of CPU and memory resources between partitions. On AIX systems only
* Support for i5/OS/IBM i, AIX and Linux

PowerVM Express

* Supported on System p520 and p550
* 3x LPARs per server

PowerVM Standard

* Supported on POWER5, POWER6, BladeCenter JS21, JS22, JS12 systems
* 10x LPARs per core
* Management via IVM and Hardware Management Console (HMC)
* Multiple shared CPU pools, allowing live load balancing of CPU resources between partitions. On POWER6 systems only.

PowerVM Enterprise

* Supported on POWER6 and BladeCenter JS22 systems
* 10x LPARs per core
* Management via IVM and HMC
* Live partition mobilty, allowing running virtual machines to migrate to another system. On POWER6 systems only.
* Multiple shared CPU pools, allowing live load balancing of CPU resources between partitions

Operating Systems

Logical partitions may run one of the following operating systems versions:Restrictions apply depending on the POWER Hypervisor technology family.
* AIX 5.2 to current release
* OS/400 v5r1 through v5r3
* i5/OS v5r4 (previously known as OS/400)
* IBM i v6r1 (previously known as i5/OS)
* SUSE SLES 9 or 10
* Red Hat Enterprise Linux 4 or 5

Other Linux distributions work but are not supported by IBM

Documentation

* [http://www-03.ibm.com/systems/p/apv/ Overview of Advanced POWER Virtualization]
* [http://www.ibm.com/developerworks/aix/library/au-aix-vioserver-v2/index.html Hands-on type article on setting up logical partitions using the Virtual I/O Server]
* [http://publib.boulder.ibm.com/infocenter/eserver/v1r3s/topic/iphcg/iphcg.pdf Virtual I/O Server Commands Reference ]

See also

* Comparison of virtual machines
* IBM AIX
* Linux on Power
* The POWER5 processor
* The POWER6 processor

External links

* [http://www.ibm.com/servers/aix/ IBM Website on AIX]
* [http://www-03.ibm.com/systems/p/ IBM Website on System p]
* [http://www.ibm.com/collaboration/wiki/display/WikiPtype/Home AIX Wiki]
* [http://www-03.ibm.com/servers/aix/6/beta.html AIX 6 Open Beta]
* [http://www-03.ibm.com/systems/power/software/virtualization/editions/index.html PowerVM Editions Formerly Advanced POWER Virtualization (APV)]
* [http://www.pseriestech.org/forum/ibm-powervm-editions/ PowerVM Editions Support]