An Exchange backup fails with an error similar to:

Error Messages -----Unable to perform backup operation, detecting that selected 'Microsoft Exchange Writer' is in failed state! 
- Writer Failure code: 0x800423f2 (VSS_E_WRITERERROR_TIMEOUT) 
- Writer ID:'76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7 


VSS_WS_FAILED_AT_FREEZE: The freeze has to do with how long application “writers” have to hold their write access to the disk. Usually that’s 60 seconds or less. Because some writers use a shorter timeout than 60 secs (Exchange is 20 seconds), the system may give freeze errors more often with disk I/O is high. Most often, this error is caused indirectly by a different application or service, and chances are that service will also log its error in the Event Viewer. Because VSS is a framework where services, such as Exchange, SQL, and Windows itself, hook into, failures such as VSS_WS_FAILED_AT_FREEZE may be caused by a configuration or resource issue. So, a Snapshot creation time under 20 seconds is also key to solve the vix error.

This indicates a critical failure of windows and is considdered unexpected behavior.  A backup from any vendor that leverages VSS for Exchange would not be successful in this state.  This could be a temporary status, or may indicate a larger configuration or even potentially corruption state of the exchange server.  Unitrends advises that after some simple tests, to immediately engage Microsoft support if this issue persists, or recover your server using BareMetal to a state when this even was not occurring.  However, the following below may be tested at your own risk:

  • Attempt to run the Exchange VSSTester scripts provided by Microsoft for VSS diagnostics.  The least this will do is confirm Unitrends itself is not causing this issue and that you have a confirmed VSS problem.  It may however lead to solutions to your issue, and is a good first step.  The scripts and documentation is located here:  (2010 - 2016 supported)
  • Reboot of the Exchange Server
  • COM+ Event System Service may need to be restarted. Root cause unknown. In some cases customers have scripted this service to restart prior to backup (if this resolves your issue we strongly encourage you to report this to Microasoft).  
  • Ensure the latest Windows and Exchange patches and hotfixes are all installed (note, some hotfixes are NOT installed via Windows Update, and may require communicating with Microsoft to determine if additional patches apply)
  • Exchange freeze is too I/O intensive on the storage and backup time and or Exchange datastore may need to be modified.
  • In some cases the database itself may be failing VSS due to integrity issues.  Create a new DB and migrate your users and attempt to back up the new database.  This is done online without disruption to users.  

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