Zmanda Cloud Backup utilizes a built-in Windows function known as Volume Shadowcopy Services, or VSS.
VSS allows backups to be taken of in-use, locked, or inaccessible files without interrupting whatever process or user is currently accessing those files. This is especially useful for databases, as it means backups can be taken while the database is active, without requiring downtime.
Every backup type in ZCB relies upon one or more VSS Writers. Each writer is controlled by a Windows Service.
A list of currently available writers can be seen via the command line on any Windows machine. Open a command prompt as an Administrator and run the command:
vssadmin list writers
This command will list all of the writers currently available on the machine as well as their current state. 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. Writers that are currently In-Progress are being used for a backup. If no backups are running, the writer may be stuck, and can be reset like Failed or Unstable writers.
Restarting the service that controls the writer will reset the writer and, in most cases, bring it back to a stable state.
It is important to note that not all controlling services can be restarted. If a service cannot be restarted, a reboot of the machine is required.
List of VSS Writers
The following list shows the VSS Writers required for each backup type, as well as the name of the controlling service.
|Backup Type||Required VSS Writer||Name of Controlling Service||Service Display Name|
|System State||ASR Writer||VSS||Volume Shadow Copy|
|BITS Writer||BITS||Background Intelligent Transfer Service|
|COM+ REGDB Writer||VSS||Volume Shadow Copy|
|IIS Config Writer||AppHostSvc||Application Host Helper Service|
|IIS Metabase Writer||IISADMIN|
IIS Admin Service
|Registry Writer||VSS||Volume Shadow Copy|
|WMI Writer||Winmgmt||Windows Management Instrumentation|
|NTDS Writer||<unknown>||Active Directory|
|Shadow Copy Optimization Writer||VSS||Volume Shadow Copy|
|Microsoft Exchange||Microsoft Exchange Writer||MSExchangeIS||Microsoft Exchange Information Store|
|Hyper-V||Microsoft Hyper-V VSS Writer||vmms||Hyper-V Virtual Machine Management|
|Microsoft SQL Server||SQL Server VSS Writer||SQL Server VSS Writer||SQL Server VSS Writer|
|MSDE Writer||MSDE Writer|
|Sharepoint||Sharepoint VSS Writer||Sharepoint VSS Writer||Sharepoint VSS Writer|
|SPSearch VSS Writer||Windows Sharepoint Services Search||SPSearch VSS Writer|
|OSearch VSS Writer||Office Sharepoint Services Search|
OSearch VSS Writer
|SPSearch4 VSS Writer||Sharepoint Foundation Search V4||SPSearch 4 VSS Writer|
|OSearch14 VSS Writer||Sharepoint Server Search 14||OSearch VSS Writer|