This article explains what the Volume Shadow Copy Service is and how it's used with Datto devices. It includes resources such as commonly found VSS writers, related services, and Microsoft resources.
- What is the Volume Shadow Copy Service?
- What is the difference between VSS backups and STC backups?
- Common VSS Writers
- Commonly Found VSS Related Services
- Microsoft VSS Resources
Microsoft's Shadow Copy Provider's: Volume Shadow Copy Service, also commonly known as VSS, are used in the process of image based backup solutions. VSS is composed of the following:
- VSS Writer: This tells the backup tool how to back up the application and its data. A VSS Writer needs to be present for the Volume Shadow Copy Service to quiesse (freeze) the program for an Application Aware backup to occur.
- VSS Requestor: This initiaties the backup process.
- VSS Provider: This allows the VSS backup process to work with the system's hardware and operating system. The VSS provider is responsible for taking a snapshot. The VSS Provider and it's associated driver are required for this snapshot to take place.
For VSS backup solutions it is important that only one process on the production machine use these VSS Writers at the same time. If more than one of these processes are running in the same environment then this will cause a conflict between the solutions resulting in the failure of one or more VSS Writers.
On Windows systems, Datto's agent-based backup software uses the Microsoft Shadow Copy Provider to perform the initial step of the backup process. In the event that an error is encountered with the Microsoft Shadow Copy Provider's VSS Writers, the ShadowSnap agent will failover to use the StorageCraft Shadow Copy Provider, referred to as the STC Backup Engine.
The STC Backup Engine provides a backup image in a crash-consistent state, such that data in processing at the time of the backup may not be saved properly.
- This is a concern for systems running any services that include a VSS writer for backups, such as database services. For instance, if the VSS writer for a database is failed, recent transactions for that database may not be backed up by ShadowSnap.
Application Aware VSS refers to the use of the Microsoft Shadow Copy Provider. This VSS Provider interacts with supported applications to provide backups as the the applications are running.
To list some of the current VSS writers on any Windows operating system, simply open the command prompt and the command:
vssadmin list writers
Below is a list of the most commonly found VSS Writers with a brief description about their individual associations to different processes:
- ADAM (instanceN) Writer: Beginning with Server 2003, this writer reports the ADAM database file (
adamntds.dit) and the associated log files for each instance in
%program files%\Microsoft ADAM\instanceN\data, where N is the ADAM instance number. These database log files are required to restore ADAM instances.
- ADAM (VMwareVCMSDS) Writer: VMWare Virtual Center Server Service for the ADAM instance VMWareVCMSDS.
- ASR Writer: Automated System Recovery which stores the BCD configuration of disks on the system on OSes starting with Vista and Server 2008.
- BITS Writer: Background Intelligent Transfer Service Writer first available in Vista and Server 2008. BITS uses the FilesNotToBackup registry key to exclude files from the BITS cache folder. The default cache location is
- Certificate Authority: This writer is responsible for enumerating the data files for the Certificate Server.
- COM+ REGDB Writer: COM+ Class Registration Database Writer responsible for the contents of the
%SystemRoot%\Registrationdirectory which was first available in Vista and Server 2008 OSes.
- DFS Replication Service Writer: Starting in Server 2003 R2, this writer protects Distributed File System Replication selections data.
- DHCP Jet Writer: Starting with Server 2003 this writer is responsible for enumerating files required for the DHCP server role. This writer is not available for workstation OSes.
- Exchange Writer: Responsible for backing up the Exchange Information Store as well as providing the ability to truncate Exchange transaction logs.
- Event Log Writer: Responsible for protecting the Event Log Viewer contents.
- FRS Writer: Responsible for the File Replication Service starting with Server 2003.
- FSRM Writer: Starting with Windows Server 2003 R2, this writer enumerates the FSRM configuration files that are used for system state backup. During restore operations it prevents changes in FSRM configuration and temporarily halts enforcement of quotas and file screens. This writer is not available for workstation OSes.
- IIS Config Writer: Protects the configuration data for Internet Information Services (IIS).
- IIS Metabase Writer: Responsible for the Microsoft Internet Information Services which is required by some SQL Server features.
- Microsoft Exchange Writer: Responsible for backing up the Exchange Information Store as well as providing the ability to truncate Exchange transaction logs.
- Microsoft Hyper-V VSS Writer: Responsible for backing up Hyper-V Virtual Machines.
- MSSearch Service Writer: Starting with Server 2008 this writer exists to delete search index files from shadow copies after creation. This is done to minimize the impact of Copy-on-Write I/O during regular I/O on these files on the shadow-copied volume.
- MSDEWriter: Beginning with Windows Server 2008, this writer exists to delete search index files from shadow copies after creation. This is done to minimize the impact of Copy-on-Write I/O during regular I/O on these files on the shadow-copied volume. This Writer is frequently called on by operations from the SQLSERVERAGENT service.
- NPS Writer: Responsible for protecting the Network Policy Server.
- NPS VSS Writer: Responsible for protecting the Network Policy Server.
- NTDS: Active Directory Domain Services VSS WriterBeginning with Windows Server 2003, this writer reports the NTDS database file (
ntds.dit) and the associated log files. These files are required to restore the Active Directory correctly.
- Search VSS Writer: Responsible for Search Operations
- Performance Counters Writer: Starting with Windows 7 and Server 2008r2, this writer reports the performance counter configuration files. These files are only modified during application installation and should be backed up and restored during system state backups and restores.
- Registry Writer: The registry writer is responsible for the Windows registry.
- SCVMM Express Writer: Responsible for the Microsoft System Center Virtual Machine Manager.
- Shadow Copy Optimization Writer: Beginning with Windows Vista and Windows Server 2008, this writer deletes certain files from volume shadow copies.
- SMS Writer: Responsible for the System Center Configuration Manager.
- SPSearch VSS Writer: Responsible for the SharePoint Server Search operation.
- SQL Server Writer: Provides added functionality for backup and restore of SQL Server, including truncation of transaction logs. Works only with instances of Microsoft SQL Server.
- System Writer: Beginning with Windows Vista and Windows Server 2008, the system writer enumerates all operating system and driver binaries.
- Task Scheduler Writer: Starting with Windows 7 and Server 2008r2, this writer reports the Task Scheduler's task files.
- TermServLicensing: Responsible for protecting the Microsoft Terminal Server Licensing.
- VSS Metadata Store Writer: Starting with Windows 7 and Server 2008r2, This writer reports the writer metadata files for all VSS express writers.
- WDS VSS Writer: Beginning with Windows Vista and Windows Server 2008, this writer reports the writer metadata files for all VSS express writers.
- WINS Jet Writer: Beginning with Windows Server 2003, this writer is responsible for enumerating files required for WINS.
- WMI Writer: Beginning with Windows Vista and Windows Server 2008, this writer is used for identifying WMI-specific state and data during backup operations.
The protected system's Windows services, commonly known as services.msc, displays the current installed services on the machine. It is important that only one process on the production machine is using the VSS writers because if there are multiple processes attempting to use them, it will cause major conflict between the solution resulting in the failure and one or more VSS writers.
The following chart indicates which VSS writers are compatible with the Datto solution.
|Acronis Nonstop Backup Service|
|Acronis Scheduler2 Service|
|Acronis Sync Agent Service|
|Background Intelligent Transfer Service|
|Backup Exec Error Recording Service|
|Backup Exec PureDisk Filesystem Service|
|Backup Exec Remote Agent for Windows|
|Backup Exec VSS Provider|
|Block Level Backup Engine Service|
|Hyper-V Volume Shadow Copy Requestor|
|Microsoft Software Shadow Copy Provider|
|MozyHome Backup Service|
|MozyPro Backup Service|
|Replay 5 SnapToVM|
Replay XML Command
SAAZCore (Current RMM Version no longer requires this, can be removed)
|StorageCraft Raw Agent|
|StorageCraft Shadow Copy Provider|
|SQL Server (BKUPEXEC)|
|SQL Server VSS Writer|
|Volume Shadow Copy|
EVault Software BUAgent
For any related VSS errors, please see the below resources provided by Microsoft:
Common Troubleshooting Steps from Microsoft Answers
Windows 2003 (some are SP1 and some are SP2)
- A Volume Shadow Copy Service (VSS) update package is available for Windows Server 2003
- A Volume Shadow Copy Service (VSS) update-2 package is available
- Availability of a Volume Shadow Copy Service (VSS) update rollup package for Windows Server 2003 to resolve some VSS snapshot issues
- Availability of Windows Server 2003 Post-Service Pack 2 COM+ 1.5 Hotfix Rollup Package 12
- Various issues may occur on a Windows Server 2003-based computer that is running the Volume Shadow Copy Service
- Time-out errors occur in Volume Shadow Copy service writers
- Optimize Shadow Copy Client accessing shadow copies in Windows Server 2003
- Parallel backup operation may fail
Windows Vista and Windows Server 2008 related
- VSS hardware snapshot database keeps growing
- Non-persistent snapshot cleanup operation is aborted
- VSS-based system state backup fails after you uninstall or upgrade a program
- Backups fail and Event ID 12293
- Memory leak in the Virtual Disk Service
- Parallel backup operation may fail
Windows Server 2008
- Cluster service may stop responding
- "VSS_E_PROVIDER_VETO" error message when you create VSS backups of multiple volumes
Windows 7 and Windows 2008 R2 related
- Snapshot may become corrupted when the Volume Shadow Copy Service (VSS) snapshot providers take more than 10 seconds to create
- Snapshot set of the VSS writer has no disk volumes
- "0x0000007E" Stop error when you run a VSS-based backup application
- Virtual machine online backup fails in Windows Server 2008 R2
- Stop error when you create a VSS snapshot backup
- Hyper-V update rollup is available for Windows Server 2008 R2
- Computer randomly stops responding after you use the VSS software provider
- A file copy operation fails when files or folders have long paths in Windows Explorer