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Are the technical terms LPAR and Virtual Machine interchangeable?

Can someone kindly differentiate between the terms LPAR and Virtual Machine? Does the term LPAR hark back to implementations of VMs back in the mainframe era, or do the two terms refer to subtly (or not so subtly) different concepts?

Topics

Information Technology

LPAR

Virtual Machine

Virtualization

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Andy Henkel

asked on Nov. 25, 2011

Damir Lukic

Owner, Virtual People Ltd.

Posted on Nov. 28, 2011

Recommended by:
Robin Goodchild

There is no difference.

LPAR means Logical Partition (on CPU), which is exactly the same thing as Virtual Machine. LPAR is registered name IBM uses for their POWER Series servers. In z-Series mainframes it's called z/VM.

Other vendors have different names. For example - HP uses nPar (for physical CPU partitioning) and vPar (for logical CPU partitioning). Difference is that nPar is used when you want to physically separate CPU's for running apps (2 CPU's for the first app, 14 CPU's for second app, 8 CPU's for third app), while vPar is used to partition CPU's logically (several 'virtual machines' will run on the same set of CPU's and use their resources, like CPU pool).

John McCoy

Solutions Architect, Perceptive Software

Posted on Dec. 1, 2011

Recommended by:
Gean Johnson

The terms LPAR and Virtual machine are not really the same thing though they are similar in concept. It’s tricky to explain this without a whiteboard and 10 minutes but I’ll try to draw out a few distinctions without getting too technical.

The term LPAR (or L-Par) is short for logical partition. A logical partition is generally implemented at (or around) the operating system level. A logical partition provides an application environment which is isolated (to varying degrees) from other environments on the same operating system. By analogy you can kind of think of LPARs as a “dorm rooms” within a building with a shared entry, kitchen, restrooms, etc.

A virtual machine on the other hand is a fully emulated machine (OS and applications) as opposed to just a section or “partition” of one. Virtual machines run in something called a hypervisor. This hypervisor looks and feels to the virtual machine like a hardware environment. By the same analogy, VMs are more like condominiums as opposed to dorm rooms. They have their own separate utilities, kitchens, restrooms, etc. and share only the building’s shell with other condos.

All things being equal, applications in an LPAR will typically outperform those in a virtual machine because there are fewer layers of abstraction in an LPAR. That said, in practice all things are not equal and the performance of virtual machines are able to approach and even exceed the performance of LPARs in most modern systems.

Damir Lukic Replied on Dec. 2, 2011

John, I believe you're partially right. Please check the following link.

http://www.ibm.com/developerworks/aix/library/au-aixhpvirtualization/index.html

"IBM uses a type-one hypervisor for its logical partitioning and virtualization, similar in some respects to Sun Microsystems' LDOMs and VMWARE's ESX server. Type-1 hypervisors run directly on a host's hardware, as a hardware control and guest operating system, which is an evolvement of IBM's classic originally hypervisor- vp/cms. Generally speaking, they are more efficient, more tightly integrated with hardware, better performing, and more reliable than other types of hypervisors. Figure 1 illustrates some of the fundamental differences between the different types of partitioning and hypervisor-based virtualization solutions. IBM LPARs and HP vPars fall into the first example -- hardware partitioning (through their logical partitioning products), while HP also offers physical partitioning through nPars."

The reference text shows IBM's comparison between IBM and HP virtualization technologies.

From the IBM's reference (quite a lot of reference links at the bottom of the page) it is pretty clear that your statement "The term LPAR (or L-Par) is short for logical partition. A logical partition is generally implemented at (or around) the operating system level. A logical partition provides an application environment which is isolated (to varying degrees) from other environments on the same operating system." is not right.

The virtualization you're explaining is more like how VMware Workstation/Server or Sun Containers work. It is not Type1 hypervisor.

John McCoy

Solutions Architect, Perceptive Software

Posted on Dec. 2, 2011

Thanks for your reply Damir.

As an IT professional, I’m sure you’re aware that the terms virtual machine and LPAR have many connotations and can mean many things depending on the context.

It seemed to me that the context of the question related was not about low-level CPU partitioning but about the concepts of partitioning an OS versus running a VM.

That said, regardless of the context, LPARs and Virtual machines are always different. Sun containers are also referred to as LPARs just as they are on IBM and HPUX machines.

Thanks again for your reply, I’m sure both of our answers have added value.

Damir Lukic Replied on Dec. 2, 2011

Hi John,

LPAR's are logical CPU partitions just as virtual machines are (typical term used in x86 virtualization). We are not talking about hardware virtual machines (as in mainframe-era) with zoned CPU's gathered together acting as one (physical partitioning - example - 3 out of 12 CPU's are Zone1). This is possible with HP nPar partitions today IIRC and it's a complete separation of resources.

So, in this case, I would say that LPAR is exactly the same thing as ESX VM, HP vPar, Sun LDOM (now Oracle VM Server). Besides these, there is Sun Container, but it's different approach, and is basically OS partitioning technique, it's not CPU partitioning.

VM or Virtual Machine is referred to CPU partitioning (using any type of hypervisor). At least that's how the term is used with the big boom of virtualization in x86 world - start of VMware in 1998.

JP Morgenthal

Principal, Ranger | Cloud & VDC Services, EMC Consulting

Posted on Dec. 2, 2011

Perception is key here. Fundamentally, they are different approaches to delivering the same capability. Today, most people equate a virtual machine with an image that represents an equivalent physical appliance. The LPAR approach is a hardware hypervisor. This leads to certain benefits that a software hypervisor cannot deliver (look for microprocessor-based virtualization to move in this direction though). However, this is not an appliance architecture, it's a utilization architecture.

Andy Henkel

Posted on Dec. 2, 2011

Hi everyone,

Firstly, thank you very much for taking the time to provide a variety of insights - all of which have been very informative and helpful.

The question arose from a document that the customer provided where they were asking about whether or not to have two separate database instances (that need to interact a lot with each other via DB links) located on the same LPAR. They also use VMWare ESX 4.1 as their hypervisor, so I wanted to gain a better understanding of the various terms in order to formulate the right questions to ask them.

- Andy

Robin Goodchild

Owner, Antarctic Technologies

Posted on Dec. 3, 2011

QUOTE: A *logical partition* provides an *application environment* which is isolated (to varying degrees) from other environments on the *same operating system*.
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Isn't this known as a sandbox? ;)

I think people (read: marketing departments) are playing with language to the point of insanity, just to try and make a product sound bigger/better than the competition, when in reality it doesn't do anything a "bare metal hypervisor" didn't do 6 years ago.