How the Instant Clone Operation Works

Stunning the Instant Clone Source Virtual Machine

When you issue the API command to initiate an instant clone operation, the host begins by doing a stun operation on the source virtual machine. The stunned condition lasts a very short time, and is not directly visible to the API user.

The stunned condition blocks all I/O operations of the source virtual machine while the instant clone is created. The stun is redundant in the case of a frozen virtual machine. During the time the source virtual machine is stunned, the host creates a delta disk for the source virtual machine, which remains empty as long as the source virtual machine is stunned or frozen.

Copying Virtual Disks During the Instant Clone Operation

Then the host creates an empty delta disk for the instant clone virtual machine. This delta disk links to the base disk of the source virtual machine. More precisely, if the source virtual machine already had one or more delta disks, the instant clone delta disk links to the second delta disk in the disk chain of the source. The second delta disk is the delta disk that was the topmost delta disk when the stun operation was invoked.

Copying Memory During the Instant Clone Operation

The host creates a new virtual memory paging file for the instant clone virtual machine, whose page tables link to the paging file of the source virtual machine. When the instant clone virtual machine is complete and is allowed to run instructions, all its memory pages will be shared with the source virtual machine until either virtual machine does a write to memory.

Configuring the Instant Clone Virtual Machine

Then the host creates a virtual machine configuration file for the instant clone, which links to its delta disk and memory paging file. At this point, the instant clone virtual machine is capable of running instructions, and the host unstuns it. Both the memory and the virtual disks are shared with the source virtual machine, so the instant clone is identical to the source virtual machine, from the guest operating system point of view.

When you create virtual machines with identical guest operating systems, the network settings conflict. Usually you will want to customize these settings and reset the network stack for each instance of the guest operating system.