Virtualization

Virtualization

1. Hypervisor

   • Thin-layer OS
   • Maps physical resources to virtual ones
   • Types
     • Type 1 Baremetal hypervisor
       • VMM layer mapped directly to hardware
         • No overheads in managing hardware
         • Reduced code duplication
     • Type 2 Host OS hypervisor
       • VMM layer on top of Host OS
         • Slow as it needs communication with Host OS for hardware sharing
   • Overcommits resources to virtual machines
     • CPU
       • Multiple CPUs mapped to multiple virtual machines
     • RAM
     • Storage
       • Virtual disks mapped to physical ones
     • Network
       • Multiple VMs connected with virtual switch
   • Allows us to run configurable VMs /legacy VMs for server requirements
   • Facilitates server consolidation by running multiple VMs in single physical hardware

2. vCenter features

   • Facilitates in managing many virtual machines
     • 10,000 VMs is the higher limit
     • 1000 physical CPUs
   • Provides central platform for creation of VMs
     • Multiple VMs created simultaneously with templates
       • Templates are read-only configurations required to initialize a virtual machine
   • Provides fault tolerance for reducing downtime
     • Fault-tolerance by snapshot
     • Fault-tolerance by cloning
       • Full clone
       • Linked clone
   • Removes the hassle of "remote-accessing" each physical resource for spawning VMs
   • Facilitates relocation through live-migration
   • Allows resource-pooling for effective spawning of VMs on underutilized physical servers
     • Many VMs doesn't utilize the resource provided to it fully
     • VM's are spawned in underutilized physical hardware to save cost
   • Provides access to any virtual machine in an ad-hoc basis

3. ESXi Architecture

   • Agentless resource management
     • Manages the underlying resource among multiple VMs
   • Agentless storage management
   • Hardware module
     • For conversion of syscall with hardware
   • Supports a thin operating system
   • CIM module