VM Backups vs Snapshots
A backup is the process of creating a consistent copy of data on a virtual machine (VM) in a virtual environment to prevent data loss. VM backups are accomplished using a conventional third party backup software.
A snapshot is a copy of the virtual machine’s (VMs) virtual machine disk (VMDK) file, at a specific point in time. Snapshots provide a change log for the VMDK and are used to restore a VM to a particular point in time when failure or errors occur. Although a snapshot does carry some traits of a backup, it is NOT a full-blown backup.
Key differences between Backups and Snapshots
A third party backup product is used to perform a VM backup.
A snapshot is useful as a short term solution for testing software with unknown or potentially harmful effects.
A backup is useful as a restoration point in the event a VM is completely corrupted or deleted.
A VM restored from a backup will have to be powered on after successful restore.
A VM reverted to a previous snapshot can already be in a powered on state.
Snapshots are NOT backups. A snapshot file is only a change log of the original virtual disk. Therefore, do not rely on it as a direct backup process. The VM is running on the most current snapshot, not the original VMDK files.
Snapshots are not complete copies of the original VMDK files. Taking a snapshot does not create a complete copy of the original VMDK file, rather it only copies the delta disks.
An excessive number of delta files in a chain (caused by an excessive number of snapshots) or large delta files may cause decreased VM and host performance.
Do not keep a single snapshot for more than 72 hours. Snapshots should not be maintained over long periods of time for application or VM version control purposes.
Do not rely upon snapshots for I/O intensive VMs with rapid data changes, because significant data inconsistencies will occur when the VM is restored.