A snapshot captures the entire state of the virtual machine at the time you take the snapshot.

Snapshots are useful when you need to revert repeatedly to the same state but you don't want to create multiple virtual machines.

A snapshot includes the following information:

Contents of the virtual machine’s memory

Virtual machine settings

State of all the virtual machine’s virtual disks

Note

VMware does not support snapshots of raw disks, RDM physical mode disks, independent disks, or of virtual machines configured with bus-sharing.

If you require bus-sharing, consider running backup software within your guest operating system as an alternative solution. If your virtual machine currently has snapshots and it is preventing you from configuring bus-sharing, delete the snapshots.

Snapshots operate on individual virtual machines. In a team of virtual machines, taking a snapshot preserves the state only of the active virtual machine.When you revert to a snapshot, you return all these items to the state they were in at the time you took that snapshot. If you want the virtual machine to be suspended, powered on, or powered off when you launch it, make sure that it is in the correct state when you take that snapshot.

While snapshots provide a point-in-time image of the disk that backup solutions can use, do not use snapshots for your own virtual machine backups. Large numbers of snapshots are difficult to manage, take up large amounts of disk space, and are not protected in the case of hardware failure.

Because you cannot revert to a snapshot with dynamic disks, quiesced snapshots are not used when backing up dynamic disks.

Backup solutions, like VMware Data Recovery, use the snapshot mechanism to freeze the state of a virtual machine. However, the Data Recovery backup method has additional capabilities that mitigate the limitations of snapshots.

Multiple snapshots refers to the ability to create more than one snapshot of the same virtual machine.

Multiple snapshots are not simply a way of saving your virtual machines. With multiple snapshots, you can save many positions to accommodate many kinds of work processes.

When taking a snapshot, the state of the virtual disk at the time the snapshot is taken will be preserved. When this occurs, the guest cannot write to the vmdk file. The delta disk is an additional vmdk file to which the guest is allowed to write. The delta disk represents the difference between the current state of the virtual disk and the state that existed at the time the previous snapshot was taken. If more than one snapshot exists, delta disks can represent the difference (or delta) between each snapshot. For example, a snapshot can be taken, and then the guest could write to every single block of the virtual disk, causing the delta disk to grow as large as the entire virtual disk.

When a snapshot is deleted, the changes between snapshots and previous disk states are merged, and all the data from the delta disk that contains the information about the deleted snapshot is written to the parent disk and merges with the base disk only when you choose to do so. This can involve a large amount of disk input and output. This may reduce the virtual machine performance until consolidation is complete.

The amount of time it takes to commit or delete snapshots depends on how much data the guest operating system has written to the virtual disks since the last snapshot was taken. The required time is directly proportional to the amount of data (committed or deleted) and the amount of RAM allocated to the virtual machine.

For additional information about snapshot behavior, see the Knowledge Base article at http://kb.vmware.com/kb/1015180.