allows for backups to be taken of files that are currently open or in use (using snapshot technology).
From the Admin Guide:
"...
The Windows Open File Backup properties specify whether a client uses Windows Open File Backup. The properties also specify whether Volume Snapshot Provider or Volume Shadow Copy Service is used as the snapshot provider.
Snapshots are a point-in-time view of a source volume. NetBackup uses snapshots to access busy or active files during a backup job. Without a snapshot provider, active files are not accessible for backup.
..."
***EDIT***
Additional documentation that may (sorry,
will!) explain it better:
About the Client Attributes properties
If you find that your client is not in the list for Client Attributes then I would add it (or any clients for that matter) as it is more than likely that it could be using VSP as its default snapshot provider. It has been proven in many instances that VSP can cause issues.