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A backup failed with an error that begins: Backup failed for too many files.

There may be additional text, such as "Check volume shadow copy services" or "The backup was canceled".

What's going on?

Sometimes, a file cannot be backed up. If too many files fail backup, ZCB will cancel the entire backup run, according to the following rules:

  • If the backup contains less than 100 files, the backup will fail if half of the files cannot be backed up.
  • If the backup contains 100 files or more, the backup will fail if more than 100 files fail to be backed up.
    • This value is configurable via the registry:
      • Locate HKEY_LOCAL_MACHINE\\SOFTWARE\\Zmanda\\ZWC\\1.0\\ENGINE\\
      • Create a new REG_DWORD key named "FailedFileCount"
      • Use DECIMAL values and input any value over 100

A list of the files that failed backup, and a link to this article, will be shown by clicking the blue exclamation point icon in the Details column of the Monitor or Report pages.


There are many possible causes for a file to fail backup. The three most common are listed below:

The files are open, locked, or in-use and located on a network shared drive

The Volume Shadow Copy Services (VSS) are a Windows component used by ZCB to take backup of open, locked, or in-use files. Unfortunately, VSS snapshots cannot be extended across a network. If a backup is taken of a network drive, backup will fail for open, locked, or in-use files


  1. Install ZCB on the network machine to take backup of the files locally. ZCB can be installed on any number of machines for no additional charge, or
  2. Schedule the backups at a time when file usage is at a minimum, or
  3. Modify the registry setting, as shown above, to raise the number of failed files to allow ZCB to complete backup of the files that are not open, locked, or in-use.

Access to file(s) is denied

All backup operations operate under the amandabackup user. The amandabackup user must have full permissions to all drives to be backed up.

Please see What is the amandabackup user? and How to use external or mapped network drives with ZCB.

The VSS Snapshot could not be created or is deleted during the backup

If a VSS snapshot cannot be created, or is deleted during the backup, ZCB will continue the backup. However open/locked files cannot be backed up without the snapshot. These files will fail, in exactly the same fashion as if they were on a network drive (see above).


Most VSS snapshot failures occur because the drive hosting the snapshot runs out of space. Common reasons for running out of space are listed below.

  1. The drive(s) may be full of files generated during everyday use:
    1. Free some space by moving or deleting excess files.
  2. Temporary files created during a backup can fill up the drive:
    1. ZCB creates temporary files during a backup. If the drive is low on space, these temp files can fill that space up and cause snapshot failures.
    2. Change the Temporary Folder in the Preferences > Advanced menu in ZCB. Then restart the services by clicking on Tools > Restart Background Services.
    3. Or, free some space on the drive(s) in question.
  3. The Windows page file may use up all of the free space:
    1. Windows uses pagefile.sys as virtual memory during memory-intensive tasks. Backups certainly qualify!
    2. The actual size of the page file varies, but can often take up many gigabytes of space.
    3. Modify the page file properties so that the page file does not fill up the drive. The page file can be reduced in size or moved to another drive.
    4. Or, free some space on the drive(s) in question.
    5. More information about page files can be found in this Microsoft article:

Snapshot errors are logged by the system. Refer to the Windows System Event logs and the Windows Application Event logs.

Also, ZCB logs may reveal more information. Please check in the BackupErrors*.txt files located in the Debug folder in your ZCB Installation Directory.