Datto SIRIS VSS Explained – Understand the Process
Microsoft Volume Shadow Copy Service, or VSS is the first process of most image based backup solutions. VSS was first made available for the Windows 2000 Operating System to create volume shadow copies. 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. Datto SIRIS ShadowSnap Agent, as well as Datto Alto and Datto Alto XL using Shadow Protect use the Microsoft Shadow Copy Provider by default to perform the inital step of the backup process. In the event that an error is encountered with the Microsoft Shadow Copy Provider’s VSS Writers, ShadowSnap will failover to use the StorageCraft Shadow Copy Provider, referred to as the STC Backup Engine. Application Aware VSS & STC Backup Engine
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.
Unlike the Microsoft Shadow Copy Provider, 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.
Below is a list of each of the most commonly found Microsoft Shadow Copy Provider’s VSS Writers and their individual associations to various processes. To list the VSS writers of any Windows OS simply open up a command prompt and enter in the command: vssadmin list writers During backup operations, VSS writers ensure that their data is quiescent and stable, suitable for shadow copy and backup.Writers collaborate with restores by unlocking files when possible and indicating alternate locations when necessary. Note: The output of the command vssadmin list writers will not list all of the following VSS Writers which appear below. It is typical for an Windows Desktop OS to display between 5-10 VSS Writers & Windows Server OS to display 10-15 VSS Writers.
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 %AllUsersProfile%\Microsoft\Network\Downloader\Cache.
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%\Registration directory 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 roleThis 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.
Commonly Found VSS Related Services
Listing of commonly found VSS-Related services that may be listed in a Protected System’s Windows Services (services.msc) as well as their compatibility to run concurrently with theShadowSnap Agent.
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.
Datto SIRIS & SIRIS Lite’s ShadowSnap Agent, as well as Datto G-Series using Shadow Protect use the Microsoft Shadow Copy Provider by default to perform the inital step of the backup process. In the event that an error is encountered with the Microsoft Shadow Copy Provider’s VSS Writers the Storage Craft’s own Shadow Copy Provider, the STC Backup Engine, automatically is failed over to & provides the backup.
VSS Hotfixes Below is a list of VSS hotfix updates that Microsoft has put out listed by OS version. Please read the articles and see if they are relevant to the server that is throwing VSS related errors. Windows XP
Optimize Shadow Copy Client accessing shadow copies in Windows XP
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
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 specific
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
For further assistance with Datto SIRIS VSS Explained please contact Invenio Support
646-395-1170
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