Creating a Snapshot

Before performing a backup operation, you must create a snapshot of the target virtual machine. Both full and incremental backup rely on the snapshot in vSphere.

With SAN transport on VMFS volumes, the virtual machine should not have any pre-existing snapshots, so that reporting of in-use disk sectors will work. For details see About Changed Block Tracking.

As a best practice, you should search for and delete any pre-existing snapshots with the same name that you selected for the temporary snapshot. These snapshots are possibly remnants from failed backup attempts.

Within a specific snapshot, the names of virtual disk files (with extension .vmdk) can be modified with a zero-filled 6-digit decimal sequence number to ensure that the .vmdk files are uniquely named. Depending on whether or not the current virtual machine had a pre-existing snapshot, the disk name for a snapshot could have this format: <diskname>-<NNNNNN>.vmdk. This unique name is no longer valid after the snapshot is destroyed, so any data for a snapshot disk should be stored in the backup program under its base disk name.

The following code sample shows how to create a snapshot on a specific virtual machine:

// At this point we assume the virtual machine is identified as ManagedObjectReference vmMoRef.
String SnapshotName = "Backup";
String SnapshotDescription = "Temporary Snapshot for Backup";
boolean memory_files = false;
boolean quiesce_filesystem = true;
ManagedObjectReference taskRef = serviceConnection.getservice().CreateSnapshotEx_Task(vmMoRef,
                           SnapshotName, SnapshotDescription, memory_files, quiesce_filesystem);

You can use the taskRef return value as a moRef to track progress of the snapshot operation. After successful completion, taskRef.info.result contains the moRef of the snapshot.