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Amount of Data to Back Up

Both the Agent for Open Files and the Enterprise Option for VSS Hardware Snap-Shot operate on a per-volume basis (VSS must prepare the entire volume for the backup before the backup operation can begin). The Agent for Open Files operates on a per-file basis (each open file is processed as it is encountered). For example, for a backup job consisting of 10 GB of critical database files that reside on a full 120 GB hard disk:

• Using the VSS solutions, a shadow copy of the entire 120 GB volume must be taken, and each Writer with data on that volume must prepare its files (both open and closed) before the backup job can begin. While the initial shadow copy may take some time, subsequent shadow copies are almost instantaneous.
• Using the Agent for Open Files, if the files to be backed up are closed when the request for the backup job is made, the backup operation can begin immediately. If there are any open files, the agent synchronizes them and allows Arcserve Backup to back them up.

For these reasons, when you are backing up a small amount of data (relative to the size of the volume on which it resides), using the Agent for Open Files to handle open files results in a much faster backup. When the amount of data to back up is large, you should use either the Agent for Open Files or the Enterprise Option for VSS Hardware Snap-Shot.