Error Message

Error from the System log of the Event Viewer on the computer being backed up:

Event ID 41

When preparing a new volume shadow copy for volume C:, the shadow copy storage on volume C: did not have sufficiently large contiguous blocks. Consider deleting unnecessary files on the shadow copy storage volume or use a different shadow copy storage volume.

From the job log of the failed backup job:

V-79-10000-11242 VSS Snapshot error. Out of disk space, or could not find an NTFS volume while creating the snapshot. Microsoft Volume Shadow Copy Service (VSS) requires an NTFS volume with enough free disk space for each physical or virtual disk volume to cache the data that changes during the backup job. Consult the Microsoft documentation for more information.

Microsoft's Volume Shadow Copy Service (VSS) can only using contiguous free disk space to create a snapshot.  If a drive does not have enough contiguous free space, VSS generates an error.

If the drive generating the error has at least several GB of free space, the first step is to run a defrag of the problem drive.   This will attempt to arrange available free space on the disk into a contiguous block.

If the errors persist, the drive may not have enough available space to allow the snapshot to be placed on itself.  In this case, VSS can be configured to write the snapshot for the problem drive to a different drive on the same computer with more available disk space.  To do this, the following procedure can be performed:

Windows Server 2008, 2008 R2, 2012, 2012 R2:
1. Open Computer in Windows Explorer on the server being backed up when the error is encountered
2. Right-click the problem drive and select "Configure Shadow Copies..."
3. Highlight the problem drive in the "Select a volume:" box
4. Click the "Settings..." button
5. Click the drop-down box for the "Located on this volume" setting.  Select a volume with more available disk space.  Also make sure "Maximum size" is set to "No limit".
6. Click OK twice

 Windows Server 2003 or 2003 R2:
1. Open My Computer on the server being backed up when the error is encountered
2. Right-click the problem drive and select "Properties"
3. Go to the "Shadow Copies" tab
4. Highlight the problem drive in the "Select a volume:" box
5. Click the "Settings..." button 
6. Click the drop-down box for the "Located on this volume" setting.  Select a volume with more available disk space.  Also make sure "Maximum size" is set to "No limit".
7. Click OK twice