VMs Virtual Machines

VM What is a VM  Virtual Machine  Software implementation of a machine running on another machine The VM may or may not resemble the host machine E.g.  Linux on a Windows machine  Windows on Windows  MVS on VM (IBM mainframe)  Linux (Intel Style) on MVS (IBM Mainframe)

Why VMs Emulate software or hardware not available  Reduce costs Reduce exposure  In a hostile environment If machine becomes infected Reboot (reload) VM  Test new environments If mess up, just reboot (reload) VM Isolate programs/environments Adjust loads  Move/Start new VM’s to new/different servers as needed

VMWare View of Benefits Compatibility:  Virtual machines are compatible with all standard x86 computers Isolation:  Virtual machines are isolated from each other as if physically separated Encapsulation:  Virtual machines encapsulate a complete computing environment Hardware independence:  Virtual machines run independently of underlying hardware

VM downside More complicated environment Need to be aware of licensing issues Virtual machine might not 100% emulate a physical machine Performance Extra cost of the VM software

VM Brief History Started on Mainframes  Late 1960’s – early 1970’s  Help develop OS for the IBM 360 and followons  Realized it could be used for “real-world” applications Became practical on PC’s in the last 10 years

VM Types System virtual machines  Have an underlying physical machine Runs one or more virtual machines  Each potentially running a different operating system  AKA hardware virtual machines Hypervisor:  Software layer providing the virtualization  AKA - virtual machine monitor Type 1 hypervisor  Runs on bare hardware  AKA - Native VM Type 2 hypervisor  Runs on top of an operating system  AKA - Hosted VM

Simple Type 2 Example Debian Image CentOS Image VM directory (/scratch) PCnn (local workstation) Debian Linux OS

Practical View of use in 302 lab

Original VM Creation NFS “Common Directory” (Read Only) install DebianCentOS /scratch PCnn (local workstation)

Each VM  Only exists on the targeted PC after installed Cannot write back to the source NFS directory  Read only How to save?

Saving VMs Every lab workstation you log onto has a network directory: network_storage  That network directory is located on the NFS server drive  That network directory will follow you to any machine in the lab you log onto Actually follows the login ID Copy the VM to the network directory and run?  Two problems: Sometimes the VM won’t work properly from an NFS Drive Changes to the VM are “permanent”  Make an error in the change  saved version now has the error  Bigger problem VM dies when workstation removed from the lab network!

Saving VMs Solution:  Make a copy of your VMs (Debian and CentOS) to your network NFS drive “One time” copy  Backup copy Put in aptly name directories:  myuseridDebian  myuseridCentOS Takes about 3-6 minutes to copy per OS  Longer if there is a lot of network traffic

Saving the VMs on local PC to network file NFS “network directory” DebianCentOS /scratch PCnn (local workstation) DebianCentOS

Saving VMs “Restoring” VM to a workstation  Copy OS image of interest From the network NFS directory To the local /scratch directory  Takes about 5 minutes to copy down Depends on network load To save changes to the VM  Think carefully: do you want to save these changes?  Copy the image back to the NFS server drive

Copying the VMs to local PC network directory DebianCentOS /scratch PCnn (local workstation) DebianCentOS

Version management When done testing a VM on the local PC  Decide if you want to save the image: Yes  Copy contents back to network directory No  Do nothing or delete entry in /scratch

USB Drives The same is true for USB drives to keep copies Advantage:  Can take home with you  Not effected if home_directory disappears Disadvantage  Can easily loose  May break

Home directory Space “Home” directory  On the desktop  On the local hard drive  a.k.a. your userid Network Directory  on the NFS server Make a copy for each OS to the Network Directory  Have about 40Gb available for your use on the NFS drive  Easily 3 OSs worth  Copy the whole directory 2 critical entries:  Name.vbox  XML file with “instructions”  Name.vdi  VM itself

Ground rules The PC’s /scratch directory is temporary  Don’t rely on contents being available next time Directories or data in /scratch may be deleted at any time  When space is needed Clean up after yourself  Get rid of any directory you are done with Remember to properly shut down VM before saving or logging off PC  May not save latest changes  May corrupt images

Sanity Rules NEVER run VM from network_storage directory  It will start  It will fail at the most critical time  It will corrupt your VM Don’t run VM from USB device  It will start  It may fail  It may corrupt your VM Start VM from its native directory  Sometimes Note: USB devices may be accessed by:  The workstation  A VM  BUT NOT BOTH at the same time! If the VM uses it the workstation will loose access!   the VM will die if you have started the VM from it!