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1.5 – Describe instant clone architecture and use cases

Instant clone uses a copy-on-write architecture similar to that of containers, which means that an app running in a child VM tries to change a shared OS file, a copy of the shared file is created and stored in the child VM. 

All modifications inside the VM are isolated within the VM itself. 

  • Master VM: Golden Image 
  • Internal Template VM: Template which is a linked clone from your golden image created when creating a desktop pool 
  • Replica: Thin provisioned full clone of the template VM. Used for read access to all the instant clone desktops
  • Parent VM: Final copy of the original VM that is used to fork the running VM’s 
  • Instant Clones VM: a running VM based on the provisioning configuration and is provisioned on demand. 

An instant clone is created from a running parent VM. Each instant clone is immediately accessible and changes to the VM don’t affect the shared data and memory of the running parent VM on which all clones are based. An instant clone requires no boot time and the running parent VM can be deleted because after creation, the clone is linked to the replica VM and not to the running parent VM. 

Instant cloning is most widely used for VDI desktops.

This differs from the cloning of VM’s directly in vSphere: 

Clone VM to Template 

  • VM can be powered on or off 
  • Provides you an option for storing the VMs virtual disks 
  • Same format as source 
  • Thin-provisioned
  • Thick-provisioned lazy-zeroed format 
  • Thick-provisioned eager-zeroed format 

Convert a template 

  • Does not offer a choice of format and leaves the VMs disk file intact 
  • Used to edit the template  

Clone a template 

Cloning a VM creates a VM that is the exact copy of the original 

  • Can be used as an alternative to deploying a VM 
  • During cloning, the VM can be powered on or off 

Cloning can only be done via vCenter Server. You cannot clone VM’s if you use VMware Host Client. Cloning a powered on VM does not automatically quiesced the services and applications of the clone VM. 

Consider the following when cloning or deploying a VM from a template: 

  • VM Templates use storage space, plan your storage accordingly 
  • Deploying a VM from a template is faster than cloning a running VM. 
  • Cloning multiple VMs from a running VM might not create identical VMs, depending on the activity within the VM when its cloned. 

OVF Templates 

You can also deploy OVF templates. OVF is a file format that supports the exchange of virtual appliances across products and platforms. These are the advantages: 

  • OVF files are compressed, allowing for faster downloads 
  • vSphere Client validates an OVF or OVA file before importing It, and ensures that it is compatible with the intended destination server. If it’s not compatible, it can’t be imported.