Virtual Machine snapshots

Virtual Machine snapshots

Virtual Machine (VM) snapshots allow you to preserve the state of the virtual machine so you can return to the same state repeatedly

Understanding Snapshots

snapshot captures the entire state of the virtual machine at the time you take it. This includes:

• Settings state : The virtual machine settings ( BIOS + .vmx )
• Disk state : The state of all the virtual machine's virtual disks.
• Memory state : The contents of the virtual machine's memory (optional). 

When you revert to a snapshot, you return all these items to the state they were in at the time you took that snapshot. 

Snapshots are useful when you need to revert repeatedly to the same state but you don't want to create multiple virtual machines or when you are going to apply changes which results you are unsure of. 

You must power off the virtual machine before taking a snapshot if the virtual machine has multiple disks in different disk modes. Also Memory cannot be snapshot'ed if any of the disks of the Virtual Machine are in independent mode. 

Although you can take an undefined amount of snapshots, VMware supports only up to 32 levels. 

When you take a snapshot, be aware of other activity going on in the virtual machine and the likely effect of reverting to that snapshot. In general, it is best to take a snapshot when no applications in the virtual machine are communicating with other computers. 

You can take a snapshot while a virtual machine is powered on, powered off, or suspended.

Using the Snapshot Manager

The Snapshot Manager lets you review all the snapshots for the active virtual machine and act on them directly. 

• The Go to command allows you to restore the state of any snapshot.
• Delete commits the snapshot data to the parent and then removes the selected snapshot.
• Delete All commits all the immediate snapshots before the You are here current state to the base disk and removes all existing snapshots for that virtual machine. 

Throughout all this document we will use delete and commit as synonyms. Do not interpret 'delete' as deleting physically a file. Why do we use delete instead of commit? Because the snapshot manager has only 2 buttons for the operation of committing snapshots and their names are 'Delete' and 'Delete all'

Snapshots configuration files

Every time a snapshot is created several files are created or updated. They are the following:

.vmsd

Snapshot descriptor file 

 

.vmsn

Snapshot settings file 

 

.vmdk and -delta.vmdk

 

Snapshot disk/delta files 

 

.vmx

VM configuration file