This article explains the Volume Shadow Copy Service, and how it interacts with the Datto backup solution. Use this article as an aid when troubleshooting backup issues.
- Datto ALTO
- Datto SIRIS
- 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
- Additional Resources
Microsoft's Shadow Copy Provider's Volume Shadow Copy Service, also commonly known as VSS, is used to take image-based backups. VSS is composed of the following:
- VSS Writer: This writer tells the backup tool how to back up the application and its data. A VSS writer must be present for the Volume Shadow Copy Service to quiesce (freeze) the program to take an application-aware backup.
- VSS Requestor: This is the writer that initiates the backup process.
- VSS Provider: This writer 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 its associated driver are required for this snapshot to take place.
For VSS backup solutions, only one process on the production machine can use the VSS writers at a time. If more than one of these processes are running in the same environment, a conflict between the solutions will happen, resulting in one or more VSS Writers failing.
On Windows systems, Datto's agent-based backup software uses the Microsoft Shadow Copy Provider to perform the initial step of the backup process. If the Microsoft Shadow Copy Provider's VSS writers encounter an error, the following will occur (depending on which agent software is in use):
- The Datto Windows Agent will fail over to the Datto Snapshot Driver, referred to as the Datto Backup Driver, bypassing the VSS backup process.
- The ShadowSnap agent will fail over to use the StorageCraft Shadow Copy Provider, referred to as the STC Backup Engine, bypassing the VSS backup process.
Both the Datto Backup Driver and the STC Backup Engine generate backups in a crash-consistent state. Data in processing at the time of the backup may not save correctly.
- Crash-consistent backups are 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 fails, recent transactions for that database may not back up.
Application-Aware VSS refers to the Microsoft Shadow Copy Provider. This VSS provider interacts with supported applications to provide backups as the applications are running.
To list current VSS writers on any Windows operating system, open an elevated command prompt and type the command:
vssadmin list writers
Below is a list of the most commonly found VSS writers with a brief description of their associations to different processes:
- ADAM (instanceName) 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: This writer handles VMWare Virtual Center Server Service for the ADAM instance VMWareVCMSDS.
- ASR Writer: This writer is the Automated System Recovery, which stores the BCD configuration of disks on the system on OSes (starting with Vista and Server 2008).
- BITS Writer: This is the 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: The COM+ Class Registration Database Writer is responsible for the contents of the directory
%SystemRoot%\Registration, which was first available in Vista and Server 2008 operating systems.
- 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: This is the writer responsible for backing up the Exchange Information Store as well as providing the ability to truncate Exchange transaction logs.
- Event Log Writer: This writer is responsible for protecting the Event Log Viewer contents.
- FRS Writer: Starting with Server 2003, this writer is responsible for the File Replication Service.
- FSRM Writer: Starting with Windows Server 2003 R2, this writer enumerates the FSRM configuration files 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: This writer protects the configuration data for Internet Information Services (IIS).
- IIS Metabase Writer: This is the writer responsible for the Microsoft Internet Information Services, which is required by some SQL Server features.
- Microsoft Exchange Writer: This writer is responsible for backing up the Exchange Information Store as well as providing the ability to truncate Exchange transaction logs.
- Microsoft Hyper-V VSS Writer: This writer backs 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, 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, and 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: The NPS Writer is Responsible for protecting the Network Policy Server.
- NPS VSS Writer: This writer protects the Network Policy Server.
- NTDS: This is the Active Directory Domain Services VSS Writer. Beginning 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: The Search VSS Writer is 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: This writer handles the Microsoft System Center Virtual Machine Manager.
- Shadow Copy Optimization Writer: Beginning with Windows Vista and Windows Server 2008, this writer deletes specific files from volume shadow copies.
- SMS Writer: This writer is responsible for the System Center Configuration Manager.
- SPSearch VSS Writer: This writer is responsible for the SharePoint Server Search operation.
- SQL Server Writer: This writer provides added functionality for backup and restore of SQL Server, including truncation of transaction logs. This writer only works 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: This writer is 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: Starting 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 identifies WMI-specific state and data during backup operations.
The following chart lists commonly-found VSS-related services and shows which are compatible with the Datto solution. You can view the VSS services installed on a Windows-based production machine by accessing the Windows Services Manager from the Start Menu, or by invoking the services.msc command from the Run prompt.
|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|
|Datto Backup Agent Service|
|EVault Software BUAgent|
|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
The following external knowledge articles provide resources for troubleshooting and optimizing VSS writers in the Windows environment.
Common VSS Troubleshooting Steps from Microsoft Answers
Windows 2003 SP1 and 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
- The startup time increases or hangs at the logon “Welcome” screen if you frequently backup Hyper-V virtual machines on a Windows Server 2008 R2 system
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 Server 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