Virtualization basics – zlinux and P series

Virtualization is the process of creating virtual version of a device or a resource. Virtualization can occur at different levels:

• Server virtualization
• Storage virtualization
• OS level virtualization
• Network virtualization
• Application virtualization

In this article we are going to discuss on zlinux and AIX P series.

Below are the common terms you hear when someone talks about AIX P series virtualization.

LPAR:

A LPAR(logical partition) can be seen as a virtual server running on a pSeries server. The LPAR can be assigned a number of available processors, relative processing power, memory and I/O devices. LPAR can have dedicated processors or virtual processors

Virtual processors:

Processing power is spread across the virtual processors. Number of virtual processors in a LPAR depends on the kind of workload it is attached to.

Dedicated processors

Dedicated processors are whole processors that are assigned to a single partition.  Atleast one processor should be assigned to a LPAR if you choose to assign dedicated processors

Below diagram (source:IBM) depicts the relationship between virtual processors and physical processing units

How is each LPAR defined ?

It is done through HMC. HMC is hardware management console which is an interface to create and manage LAPRs. Below is a sample definition of LPAR

Min VPs   Desired VPs  Max VPs   Min PU    Desired PU   Max PU     Capped/Uncapped

1                     2                     4                     0.1        2.0                 4.0                             Y

 

Min VPs—Minimum Virtual processors

Desired VPs – Desired number of virtual processors

MaxVPs – Maximum number of virtual processors.

Capped/Uncapped – Can it used shared pool or not ?

Min PU – Minimum Processing Units

Desired PU – Desired processing units

Max PU – Maximum processing units

Shared processor pool

The POWER Hypervisor schedules shared processor partitions from a set of physical processors that is called the shared processor pool. By definition, these processors are not associated with dedicated partitions.

SMT(Simultaneous multi threading)

Virtual processor can have one , two or four logical processors. In POWER7 systems processor enables execution of 4 threads simultaneously. SMT increases the throughput for a given amount of hardware.  SMT allows instructions from more than one thread to be executed simultaneously on the processor

Capped/Uncapped – In uncapped Processing capacity can exceed the entitled CPU allocated whereas in capped processing capacity does not exceed entitled CPU

What is uncapped weight — Uncapped weight can be in the range of 0-255 . Default uncapped weight is 128.When there is a competition for resources , additionalcapacityshare  is calculated by dividing uncapped weight by sum of all the uncapped weights of the uncapped parititions

Entitled capacity: Number of processing units that a LPAR is entitled to receive. These are guaranteed for the LPAR. It is important to monitor this element

Below diagram will give you a complete overview:

 

1)You can see the physical cores which are virtualized using hypervisor

2)Pool #1 , Pool #2 and Pool #3 are shared processor pools

3)LPAR#1 and LPAR#2 have dedicated processors

4)SPLPAR= Shared processor LPAR

5)SPLPAR#3 has SMT ON and each VP two logical processors

6)SLPAR #4 is capped LPAR meaning it can not used shared processor pool is it needs additional help.

 

Monitoring:

1)Lparstat command is a good utility to monitor the LPARS

Example:

Lparstat 5 5

Lparstat –i

2)nmon ,SAR

 

zlinux – Linux on system Z

 

zLinux: Linux on System z is the collective term for the Linux operating system compiled to run on IBM mainframes, especially System z machines. Other terms with the same meaning include Linux on zEnterprise 196, Linux on System z10, Linux on System z9, Linux on zSeries, Linux/390, zLinux, z/Linux, etc.(source:Wikipedia)

LPAR: A physical machine can be separated into several logical partitions each hosting a separate OS. LPARs are managed by PR/SM faciity. A single mainframe machine can be divided into as many as 60 LPARs. The partitions could be assigned dedicated or shared processors to do their work and also to use any unused CPU cycles of other processors if they were not being fully utilized.

z/VM: z/VM provides additional virtualization on top of the LPARs. Control program (CP) has all the software modules that makeup the core of z/VM. The virtualization technology found in z/VM is unique because it allows a guest to have a full functioning system without having complete control of the hardware resources.  This allows z/VM’s virtualization technology to share its limited resources with as many guests as needed.  z/VM uses the real resources at its disposal (processors, memory, I/O devices, and networks) to create virtual machines, each able to run its own, independent copy of any operating system that supports the zSeries architecture (which includes Linux).  An operating system running in a virtual machine does so as if it were executing on real hardware.  Hardware architecture and facilities are presented to the “guest” system by z/VM in such a way that the guest operating system believes it is using a real system, not a virtual one. This is an illusion that the virtual machines possess.  Therefore, virtualization technology creates an illusion that z/VM uses to virtualize hardware components.(Source: IBM docs)

IFL : The Integrated Facility for Linux (IFL) is a processor dedicated to running the linux operating system, with or without z/VM. IFLs are one of three types of IBM mainframe processors expressly designed to reduce software costs.

Below diagram illustrates zlinux architecture. You can see the two levels of virtualization . LPARs are again divided into guests with the help of z/VM

Advantages with zlinux :

1)      Licensing costs

2)      Management  of infrastructure