z/VM and z/Linux is like biscuits and gravy

    Some things are just better  together.


    Mmmm.... Of course that’s a complete dramatization, but  you get the point.  


    As I indicated in my last post, virtualization is a  requirement for many reasons. Today's System z mainframe has it built in. Each  machine has a type 1 Hypervisor built in to transform physical resources into  virtual ones. Infact, System P and I models are equipped with Hypervisor  technology as well.  Also virtualizations of memory, etc has been around  in operating systems for years. Yes, z/VM, a virtual machine OS, facilitates  z/Linux installations. But, how? Why wouldn't I just want want to use a PR/SM  setup instead? The answer is related to how many Linux machines do you need as  well as other considerations we will be discussing in this  article.  


    PR/SM (Processor Resource/Systems Manager) of  course is derived from VM technology and is included with your z series  processor. By creating Logical partitions, it also allows these LPARS to share  processor and I/O resources by using MIF (Multiple Image Facility) and MCSS  (multiple channel subsystem). These components allow I/O channel paths and  subsets of devices attached to those paths to be shared between LPARS. PR/SM has  improved over the years and allows for dynamic LPAR; the ability to add and  delete processors, memory, and I/O between LPARS while they are still  active. 


    So why not just use this instead of paying of z/VM?  This answer can be related to the trade off of managing a variety of LPAR  (logical partition) configurations. You need to get the right mix of LPARs and  massage them so that they will not have underutilized resources allocated to  them. There is also a current limit in PR/SM of 60 LPARS.  


    One of the reasons for virtualization I indicated  earlier was if you want to drive up resource utilizations. Of course you could  make OS images more application complex by consolidating. This had been done  before on Mainframes. Yet, there were many reasons for moving applications to  other machines. In the old days of MVS, you might have had a problem with IMS  and DB2 co-existing well in shared memory. The distributed environment was also  moving applications to their own servers with regard to change  control or machine stability. Ultimately, this drove up the number of  underutilized machines. With larger number of servers being used, there begins a  boundary where one type 1 Hypervisor VM (PR/SM) or another one like z/VM may be  more appropriate to a given shop. 


    Here is but a few of Z/VM's  advantages:


    • More VM:  Hundreds of VMs can be run under one z/VM. The number of VMs that you can run is  limited only by the amount of system resources available.

    • Starts  everything: Either in System Config file or using the System userid for startup  "autolog1", the VM administrator can define resources and start  the Linuxes.

    • Dynamic  reallocation: Using execs, PROP, or Performance Toolkit, the VM administrator  can have a wide range of on-demand allocation of resources as needed including  setting the share priorities of the Linuxes as well as monitoring and  reporting.

    • Over-allocation: Because of virtualization of memory  for example, the over-allocation of resources is handled by z/VM as  paging.

    • Upgrade in  place: With shared resources like disks, Linux upgrades can be easily handled by  add/replace with larger or more disks.

    • Vswitch  controller: z/VM's TCP/IP stack initializes the OSA-Express device and continues  communication as guest host couples to the virtual switch. In the event of OSA  failures, the Linuxes can be isolated from the recovery that z/VM provides with  the TCP/IP stack as this controller switches to alternate OSA. Recoveries can be  even be more robust with controller failures being replaced by another  controller. Starting with z/VM 5.3 there is support for IEEE 802.3ad Link  Aggregation, Vswitch management (SNMP), native VLAN, improved diagnostics with  Diagnose x'26c', etc. 


    At the IBM Infocenter, they write, "virtualization  can improve IT resource utilization by allowing system administrators to access  and manage resources across a homogenous and heterogeneous environment."  In  short, depending on your installation, virtualization is a given and PR/SM may  be just fine. However, z/VM may be just the ticket for those shops that would  like to take advantage of many of its features. As a Linux administrator and  z/VM offering the ability to have any volume available to any Linux, mmmm  tasty in deed.  I will talk more about that in latter posts.  Stay in  Touch....