VSS or Volume Shadow Service is a service on Windows machines that is used to take a snapshot of data while it's being used. This allows applications using the service to make a copy of files, even if they're locked for use. VSS copies the data under the hidden “System Volume Information” folder of the disk until the data is removed by a process or a retention period on the disk. Each service that utilizes a vss writer has a service dedicated to it

Most Backup solutions on windows utilize the features of Windows VSS to create backups and then use the vss copy to transfer the data, allowing the backup to continue at a faster rate than normal. VSS has the potential to have problems and rarely tells you what went wrong.

Use the following command to view all vss writers on the system (needs to be done from an administrative command prompt/powershell session) vssadmin list writers This will give you a list of all writers on the system, search for writers that aren't stable or show errors. Use the following link to determine which writer is failing and which service is responsible for the behaviour of the writer. http://www.planetcobalt.net/sdb/vss_writers.shtml

Locate the service attached and determine if it's appropriate to restart the service (will you crash anything if the service goes down)

  If appropriate restart the service.
  If not appropriate, it may require a reboot of the whole machine to bring the service online