This article is for Amanda Enterprise (AE)
About VSS and VSS Writers
Zmanda Windows Client (ZWC) utilizes a set of built-in Windows functions known as Volume Shadowcopy Services, or VSS, to create snapshots of data for backup.
Most backup types have a specific VSS Writer that is explicitly designed for backup and restore of that specific type of data. For example, there is a SQL Server Writer that is used for backup and restore of Microsoft SQL Server databases.
Some backup types have a single writer, while others have multiple writers. Every writer is controlled by a Windows Service.
The VSS Writers are used by many different applications. Nearly all Windows backup applications, ZWC included, interface with the VSS Writers, as will certain built in Windows features that are not necessarily backups. For example, the System Restore functionality in Windows uses VSS to create restore points so that users can roll back to a known good configuration.
A ZWC backup may fail and report any of the following errors:
- One or more of the VSS Writers required for backup have failed. Please restart <service>.
- One or more of the VSS Writers required for System State have failed. Please reboot the system.
- One or more of the VSS Writers required for backup are currently in use by another process.
This is due to the failure of a VSS writer. If a writer has failed, all operations for all applications that rely on that writer will fail.
It is possible to check the state of all writers on the system using the vssadmin list writers command.
Note: If this error appears during Differential or Incremental backups of databases, please review the following article instead: Databases and Multiple Backup Applications
This behavior accounts for an overwhelming majority of VSS Writer issues related to Microsoft SQL Server, Microsoft Exchange, and Microsoft SharePoint.
Warning: Some VSS Writers are tied to services that directly impact the functionality of an application. For example, the Exchange VSS Writer is controlled by the Microsoft Exchange Information Store (MEIS) service. Exchange cannot send or receive email while the MEIS service is disabled. Therefore restarting MEIS will result in an interruption of email functionality.
In most cases, this interruption is brief.
vssadmin list writers
The vssadmin list writers command will list all of the writers currently available on the machine as well as their current state. Run vssadmin list writers from an elevated (Run As Administrator) Command Prompt.
In most situations, each writer will be in one of these three states:
- A writer in the Stable state is ready and waiting to take a backup.
- Writers in the Failed or Unstable states have encountered a problem, and may need to be reset by restarting the controlling service.
- Writers that are currently Waiting for Completion or In-Progress are in use by some process. Cancel any backup that is running, or wait for it to complete, before running a new backup.
- If no backups are running, the writer should be reset like Failed or Unstable writers by restarting the controlling service.
How to Resolve This Error Message
There are many possible reasons that a VSS Writer can fail. The writer must be brought back to the Stable state before backups can function.
In most cases, stabilizing a writer is as simple as restarting the service that controls the VSS Writer. In others, there is a well-known and understood issue that causes the VSS Writer to fail.
Additionally, most backup types have specific requirements that must be met. For example, Microsoft Exchange Server backups require that Circular Logging be disabled. If Circular Logging is not disabled, the VSS Writer will fail during Incremental and Differential backups.
All requirements are listed in the Zmanda Windows Client User Manual.
Verify that all requirements are met before moving on to the solutions below.
Solution #1: Restart the Controlling Service
Most failed VSS Writer issues can be fixed with a simple restart of the service that controls the writer. This usually brings the writer back to its stable, working state.
Use vssadmin list writers to check which writers have failed. Compare the results with the list of writers and their controlling services at Info: List of VSS Writers and Services.
Once you’ve discovered the controlling service, open the Windows Services panel, Services.msc. Locate the controlling service and restart it.
Once the service has been restarted, run vssadmin list writers again to see if the writer is now Stable. If it is, attempt the backup again.
Should the backup still fail, or if the writer is still not Stable, please check our Knowledgebase for related articles and known VSS issues.
Note: Some services cannot be restarted while the system is running. A reboot of the machine is required to reset the writers tied to services that cannot be restarted.
For example, the writers associated with System State backups usually cannot be restarted and thus require a reboot of the system.
Warning: Some VSS Writers are tied to services that directly impact the functionality of an application. For example, the Exchange VSS Writer is controlled by the Microsoft Exchange Information Store (MEIS) service. Exchange cannot send or receive email while the MEIS service is disabled. Therefore restarting MEIS will result in an interruption of email functionality.
In most cases, this interruption is brief.
For Microsoft Exchange Information Store (MEIS) Service
The VSS Writer could fail if you were attempting to perform an incremental or differential backup after adding a new Storage Group to Exchange, without first performing a new full backup with Amanda Enterprise.
Please follow these steps to resolve this issue:
- Restart the Microsoft Exchange Information Store service.
- Then, perform a new full backup of your Exchange Database backup set. This will ensure that all Storage Groups, including the new one have a full backup on record.
- After the full backup is complete, the incremental and differential backups will succeed.
Solution #2: Check for Known VSS Issues
Certain specific VSS Writer failures are well understood. These failures are discussed in our Knowledgebase.
- Databases and Multiple Backup Applications
- Troubleshooting SQL VSS Writer Issues
- System State Backups Fail and Event ID 8194 is Logged
Solution #3: Verify that Windows and the Application to be Backed Up are Both Fully Up-to-Date
Microsoft has released many updates, patches, and hotfixes for VSS-related issues. Although this applies to all versions of Windows, the updates are most relevant to Windows Server 2003.
Some applications, such as Microsoft Exchange, may also have updates related to backup, restore and VSS.
Please ensure that the system is fully up to date.
Solution #4: Verify System Health
VSS functionality can be compromised by failing hardware on the system. Problems with disk storage (such as full disks, failing disks, damaged RAID arrays, and the use of 4k drives on older systems) are particularly likely to cause VSS failures. However, hardware issues of any type can potentially impact the ability of the system to take snapshots using the VSS Writers.
If any problems are discovered, resolve them before attempting backups again.
Further Troubleshooting
If none of the above information applies, the system and the VSS failures should be thoroughly investigated by the System Administrator for the system in question. The Windows Application Events and Windows System Events usually contain information about writer failures.
The VSS Writers are Windows functions. Amanda Enterprise and Zmanda Windows Client simply call upon the writers at backup time. As such, the system administrator for the Windows system(s) involved should investigate further.
