Editing Shadow Copy

{{Short description|Microsoft technology for storage snapshots}}
{{Use dmy dates|date=May 2015}}
{{Infobox software
| name = Shadow Copy
| screenshot = Previous Versions Vista.png
| screenshot_size = 300px
| caption = ''Previous Versions'' in [[Windows Vista]], a part of [[Windows Explorer]] that allows persistent shadow copies to be created
| developer = [[Microsoft]]
| other_names = {{Plainlist|
*Volume Snapshot Service<ref name=VSS-symantec-glossary>{{cite web|title=Volume Snapshot Service (VSS)|url=http://www.symantec.com/security_response/glossary/define.jsp?letter=v&word=volume-snapshot-service-vss|archive-url=https://web.archive.org/web/20160513111005/https://www.symantec.com/security_response/glossary/define.jsp?letter=v&word=volume-snapshot-service-vss|url-status=dead|archive-date=13 May 2016|work=Glossary|publisher=Symantec|access-date=2 May 2013}}</ref>
*Previous Versions
*Shadow Copies for Shared Folders8
*VSS<ref name=VSS-msdn>{{cite web|title=Volume Shadow Copy Service Overview|url=http://msdn.microsoft.com/en-us/library/windows/desktop/aa384649%28v=vs.85%29.aspx|work=[[MSDN#Library|MSDN Library]]|publisher=Microsoft|access-date=2 May 2013|date=5 November 2012}}</ref> 
  }}
| service_name = VSS<ref name=VSS-msdn />
| operating system = [[Microsoft Windows]]
}}
'''Shadow Copy''' (also known as '''Volume Snapshot Service''',<ref name=VSS-symantec-glossary /> '''Volume Shadow Copy Service'''<ref name=VSS-msdn /> or '''VSS'''<ref name=VSS-msdn />) is a technology included in [[Microsoft Windows]] that can create backup copies or [[Snapshot (computer storage)|snapshots]] of [[computer file]]s or [[volume (computing)|volumes]], even when [[File locking|they are in use]]. It is implemented as a [[Windows service]] called the ''Volume Shadow Copy'' service. A software ''VSS provider'' service is also included as part of Windows to be used by Windows applications. Shadow Copy technology requires either the Windows [[NTFS]] or [[ReFS]] filesystems in order to create and store shadow copies. Shadow Copies can be created on local and external (removable or network) volumes by any Windows component that uses this technology, such as when creating a scheduled [[Windows Backup]] or automatic [[System Restore]] point.

==Overview==
VSS operates at the [[Block (data storage)|block level]] of volumes.

A snapshot is a read-only point-in-time copy of the volume. Snapshots allow the creation of consistent backups of a volume, ensuring that the contents do not change and are not [[file locking|locked]] while the backup is being made.

The core component of shadow copy is the Volume Shadow Copy [[Windows service|service]], which initiates and oversees the snapshot creation process. The components that perform all the necessary data transfer are called ''providers''. While Windows comes with a default System Provider, software and hardware vendors can create their own software or hardware providers and register them with Volume Shadow Copy service. Each provider has a maximum of 10 seconds' time to complete the snapshot generation.<ref name=How-TechNet>{{cite web |url=https://technet.microsoft.com/en-us/library/cc785914(WS.10).aspx |title=How Volume Shadow Copy Service Works |work=[[Microsoft TechNet|TechNet]] |publisher=Microsoft |date=28 March 2003 |access-date=4 January 2011 }}</ref>

Other components that are involved in the snapshot creation process are ''writers''. The aim of Shadow Copy is to create consistent reliable snapshots. But sometimes, this cannot simply be achieved by completing all pending file change operations. Sometimes, it is necessary to complete a series of inter-related changes to several related files. For example, when a database application transfers a piece of data from one file to another, it needs to delete it from the source file and create it in the destination file. Hence, a snapshot must not be between the first deletion and the subsequent creation, or else it is worthless; it must either be before the deletion or after the creation. Enforcing this semantic consistency is the duty of writers. Each writer is application-specific and has 60 seconds to establish a backup-safe state before providers start snapshot creation. If the Volume Shadow Copy service does not receive acknowledgement of success from the corresponding writers within this time-frame, it fails the operation.<ref name=How-TechNet />

By default, snapshots are temporary; they do not survive a reboot. The ability to create persistent snapshots was added in Windows Server 2003 onward. Windows 8 removed the GUI portion necessary to browse them, but it was restored in later Windows versions. ({{section link||History}})

Windows software and services that support VSS include [[Windows Server Failover Clustering|Windows Failover Cluster]],<ref>{{cite web|url=https://technet.microsoft.com/en-us/library/cc770625(v=ws.10).aspx|title=What's New in Failover Clusters in Windows Server 2008|last=Archiveddocs|website=technet.microsoft.com|access-date=18 March 2018}}</ref> Windows Server Backup,<ref>{{Cite web|url=https://docs.microsoft.com/en-us/windows-server/storage/file-server/volume-shadow-copy-service|title=Volume Shadow Copy Service|last=JasonGerend|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> [[Hyper-V]],<ref>{{Cite web|url=https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/integration-services|title=Hyper-V Integration Services|last=scooley|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> [[Microsoft Virtual Server|Virtual Server]],<ref>{{Cite web|url=https://docs.microsoft.com/en-us/virtualization/community/team-blog/2007/20070716-microsoft-virtualization-and-virtual-server-2005-r2-sp1|title=Microsoft Virtualization and Virtual Server 2005 R2 SP1|last=scooley|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> [[Active Directory]],<ref>{{Cite web|url=https://docs.microsoft.com/en-us/windows/win32/vss/vss-backup-and-restore-of-the-active-directory|title=VSS Backup and Restore of the Active Directory - Windows applications|last=mcleanbyron|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> [[Microsoft SQL Server|SQL Server]],<ref>{{Cite web|url=https://docs.microsoft.com/en-us/biztalk/core/sql-server-database-mirroring-volume-shadow-copy-service-and-alwayson|title=SQL Server database mirroring, Volume Shadow Copy service and AlwaysOn - BizTalk Server|last=MandiOhlinger|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> [[Microsoft Exchange Server|Exchange Server]]<ref>{{Cite web|url=https://docs.microsoft.com/en-us/exchange/high-availability/disaster-recovery/disaster-recovery|title=Exchange Server data protection, Exchange disaster recovery, Exchange backup, Exchange VSS Writer, VSS Backup Exchange, Exchange Server data recovery, Exchange data recovery|last=msdmaguire|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref> and [[Microsoft SharePoint|SharePoint]].<ref>{{Cite web|url=https://docs.microsoft.com/en-us/sharepoint/dev/general-development/how-to-back-up-and-restore-a-search-service-application-in-sharepoint-using|title=Back up and restore a search service application in SharePoint using VSS|last=spdevdocs|website=docs.microsoft.com|language=en-us|access-date=2019-08-11}}</ref>

The end result is similar to a [[versioning file system]], allowing any file to be retrieved as it existed at the time any of the snapshots was made. Unlike a true versioning file system, however, users cannot trigger the creation of new versions of an individual file, only the entire volume. As a side-effect, whereas the owner of a file can create new versions in a versioning file system, only a [[system administrator]] or a backup operator can create new snapshots (or control when new snapshots are taken), because this requires control of the entire volume rather than an individual file. Also, many versioning file systems (such as the one in [[OpenVMS|VMS]]) implicitly save a version of files each time they are changed; systems using a snapshotting approach like Windows only capture the state periodically.

==History==
{{Update|section|date=August 2015}}

===Windows XP and Server 2003===
''Volume Snapshot Service'' was first added to Microsoft Windows in [[Windows XP]]. It can only create temporary snapshots, used for accessing stable on-disk version of files that are opened for editing (and therefore locked). This version of VSS is used by [[NTBackup]].

The creation of persistent snapshots (which remain available across reboots until specifically deleted) has been added in [[Windows Server 2003]], allowing up to 512 snapshots to exist simultaneously for the same volume. In Windows Server 2003, VSS is used to create incremental periodic snapshots of data of changed files over time. A maximum of 64 snapshots are stored on the server and are accessible to clients over the network. This feature is known as ''Shadow Copies for Shared Folders'' and is designed for a [[client–server model]].<ref>{{cite web|title=Shadow Copy Client Download|url=https://technet.microsoft.com/en-us/windowsserver/bb405951.aspx|website=[[Microsoft TechNet|TechNet]]|publisher=[[Microsoft]]|access-date=21 October 2014}}</ref> Its client component is included with Windows XP SP2 or later, and is available for installation on [[Windows 2000]] SP3 or later, as well as Windows XP RTM or SP1.<ref>{{cite web |url=http://blogs.msdn.com/adioltean/archive/2004/12/17/323742.aspx |title=Tips for deploying Shadow {{sic|copies|nolink=yes}} for Shared Folders |date=17 December 2004 |access-date=21 April 2009 |last=Oltean |first=Adi |work=Antimail |publisher=[[Microsoft]] }}</ref>

{{Infobox software
| name = vssadmin
| logo = 
| screenshot = 
| screenshot size = 
| caption = 
| developer = [[Microsoft]]
| released = 
| latest release version = 1.1
| latest release date = 
| operating system = [[Microsoft Windows]]
| genre = [[Command (computing)|Command]]
| license = [[Proprietary software|Proprietary]] [[commercial software]]
| website = {{URL|https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/vssadmin}}
}}
Windows XP<ref name="msdn article">{{cite web |title=Windows XP - Volume Shadow Copy Service |url= http://msdn.microsoft.com/en-us/library/windows/desktop/bb968832(v=vs.85).aspx |work=[[MSDN]] |publisher= [[Microsoft]] |access-date= 31 May 2013}}</ref> and later include a command line utility called <code>vssadmin</code> that can list, create or delete volume shadow copies and list installed shadow copy writers and providers.<ref>{{cite web |url = https://technet.microsoft.com/en-us/library/cc754968.aspx  |title = Vssadmin  |work = Windows Server 2008 and Windows Server 2008 R2 documentations. [[Microsoft TechNet|TechNet Library]] |at = Windows Server Commands, References, and Tools  |publisher = Microsoft |date = 28 September 2007 |access-date = 27 March 2012}}</ref>

===Windows Vista, 7 and Server 2008 ===
Microsoft updated a number of Windows components to make use of Shadow Copy. [[Backup and Restore]] in [[Windows Vista]], [[Windows Server 2008]], [[Windows 7]] and [[Windows Server 2008 R2]] use shadow copies of files in both file-based and sector-by-sector backup. The ''System Protection'' component uses VSS when creating and maintaining periodic copies of system and user data on the same local volume (similar to the Shadow Copies for Shared Folders feature in Windows Server); VSS allows such data to be locally accessed by [[System Restore]].

System Restore allows reverting to an entire previous set of shadow copies called a ''restore point''.<ref>
Compare:{{cite web
| url            = http://answers.microsoft.com/en-us/windows/forum/windows_vista-files/information-about-spp-folder-in-windows-vista/f050c2c8-2e8f-4092-9012-cd42c26ac18f?auth=1
| title          = Information about SPP folder in Windows vista 
| date           = 2010-08-20
| website        = Microsoft Community
| publisher      = Microsoft
| access-date    = 2015-07-22
| quote          = SPP stand for Shared Protection Point and is used by windows to store information on restore point.
}} 
</ref><ref>
Compare:
{{cite web
 |url= https://blogs.technet.microsoft.com/filecab/2009/09/16/diagnosing-failures-in-windows-server-backup-part-1-vssspp-errors/
 |title= Diagnosing Failures in Windows Server Backup – Part 1 (VSS/SPP Errors)
 |last= Barreto
 |first= Jose
 |date= 2009-09-16
 |website= Storage at Microsoft: The official blog of the Windows and Windows Server storage engineering teams
 |publisher= Microsoft Corporation
 |access-date= 2017-09-11
 |quote= [...] the origin of the error is in an underlying layer such as Volume Shadow Copy Service (VSS), Shared Protection Point (SPP), or other applications that plug into VSS framework.
}}
</ref>
Prior to Windows Vista, System Restore depended on a file-based filter that watched for changes to files with a certain set of extensions, and then copied files before they were overwritten.<ref>{{cite book |last1= Russinovich |first1= Mark E. |first2= David A. |last2= Solomon |title= Microsoft Windows Internals: Microsoft Windows Server 2003, Windows XP, and Windows 2000 |year= 2005 |publisher= [[Microsoft Press]] |location= [[Redmond, WA]] |isbn= 0-7356-1917-4 |edition= 4 |pages= [https://archive.org/details/isbn_9780735619173/page/706 706–711] |url-access= registration |url= https://archive.org/details/isbn_9780735619173/page/706 }}</ref><ref>{{cite web|title= Windows Backup|url= http://www.microsoft.com/middleeast/windowsvista/features/foreveryone/backup.mspx|work= Windows Vista portal|publisher= [[Microsoft]]|access-date= 11 January 2014|archive-url= https://web.archive.org/web/20070510204203/http://www.microsoft.com/middleeast/windowsvista/features/foreveryone/backup.mspx|archive-date= 10 May 2007}}</ref><ref name="BackupGuide">{{cite journal|last= Fok|first= Christine|title= A Guide to Windows Vista Backup Technologies|url= https://technet.microsoft.com/en-us/magazine/2007.09.backup.aspx|journal= TechNet Magazine|publisher= [[Microsoft]]|access-date= 11 January 2014|date= September 2007}}</ref> In addition, a part of [[Windows Explorer]] called ''Previous Versions'' allows restoring individual files or folders locally from restore points as they existed at the time of the snapshot, thus retrieving an earlier version of a file or recovering a file deleted by mistake.

{{Infobox software
| name                   = diskshadow
| logo                   = 
| screenshot             = 
| screenshot size        = 
| caption                = 
| developer              = [[Microsoft]]
| released               = 
| latest release version = 
| latest release date    = 
| operating system       = [[Microsoft Windows]]
| genre                  = [[Command (computing)|Command]]
| license                = [[Proprietary software|Proprietary]] [[commercial software]]
| website                = {{URL|https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/diskshadow}}
}}
Finally, Windows Server 2008 introduces the <code>diskshadow</code> utility which exposes VSS functionality through 20 different commands.<ref>{{Cite web
 |url = https://technet.microsoft.com/en-us/library/cc772172%28WS.10%29.aspx
 |title = Diskshadow
 |work = Windows Server 2008 and Windows Server 2008 R2 documentations. [[Microsoft TechNet|TechNet Library]]
 |at = Windows Server Commands, References, and Tools
 |publisher = Microsoft Corporation
 |date = 28 September 2007
 |access-date = 27 March 2012
}}</ref>

The system creates shadow copies automatically once per day, or when triggered by the backup utility or installer applications which create a restore point.<ref>{{cite web
 |url= https://technet.microsoft.com/en-us/library/cc749185.aspx 
 |title= Selected Scenarios for Maintaining Data Integrity with Windows Vista
 |work= TechNet
 |publisher= Microsoft Corporation
}}</ref><ref>{{cite web |url= https://technet.microsoft.com/en-us/magazine/2007.09.backup.aspx|title= A Guide to Windows Vista Backup Technologies|publisher= Microsoft}}</ref> The "Previous Versions" feature is available in the Business, Enterprise, and Ultimate [[Windows Vista editions | editions of Windows Vista]]<ref>{{cite web
 |url= http://www.microsoft.com/windows/products/windowsvista/footnotes.mspx 
 |title= Volume Shadow Copy and "Previous Versions" feature in Windows Vista
 |publisher= Microsoft Corporation
}}</ref> and in all [[Windows 7 editions]]. The Home Editions of Vista lack the "Previous Versions" feature, even though the ''Volume Snapshot Service'' is included and running. Using third-party tools it is still possible to restore previous versions of files on the local volume.<ref>
[http://www.shadowexplorer.com/ ShadowExplorer allows restoring lost or altered files]
</ref>
Some of these tools also allow users to schedule snapshots at user-defined intervals, configure the storage used by volume-shadow copies and compare files or directories from different points-in-time using snapshots.<ref>
[http://www.bearsontheloose.com/ TimeTraveler adds a timeline to Windows Explorer allowing the user to open, restore or compare files or directories from points-in-time]
</ref>
Windows 7 also adds native support through a GUI to configure the storage used by volume-shadow copies.

===Windows 8 and Server 2012===
While supporting persistent shadow copies, [[Windows 8]] lacks the GUI portion necessary to browse them; therefore the ability to browse, search or recover older versions of files via the ''Previous Versions'' tab of the ''Properties'' dialog of files was removed for local volumes. However, using third party tools (such as ShadowExplorer) it is possible to recover that functionality.  The feature is fully available in [[Windows Server 2012]].<ref>{{cite web|url=http://msdn.microsoft.com/en-us/library/windows/desktop/hh848072%28v=vs.85%29.aspx|title=Previous versions UI removed for local volumes (Windows)|access-date=17 November 2012}}</ref>

===Windows 10===
Windows 10 restored the Previous Versions tab that was removed in Windows 8; however, in earlier builds it depended upon the File History feature instead of Volume Shadow copy.  Current builds now allow restoration from both File History and System Protection (System Restore) points, which use Volume Shadow Copy.<ref>{{cite web |last1=Saluste |first1=Margus |title=File History in Windows 8, 8.1 and 10 |url=https://www.winhelp.us/file-history-in-windows-8.html |website=WinHelp.us |access-date=18 March 2018 |archive-url=https://web.archive.org/web/20201225185236/https://www.winhelp.us/file-history-in-windows-8.html |archive-date=25 December 2020 |url-status=dead}}</ref>

=== Windows 11 ===
Windows 11 retains the same Previous Versions and File History feature introduced in Windows 10, although it is disabled by default.<ref>{{Cite web |last=Huc |first=Mauro |date=2023-03-08 |title=How to enable Previous Versions to recover files on Windows 11 - Pureinfotech |url=https://pureinfotech.com/enable-previous-versions-windows-11/ |archive-url=https://web.archive.org/web/20230527181204/https://pureinfotech.com/enable-previous-versions-windows-11/ |archive-date=May 27, 2023 |access-date=2023-07-19 |website=Pureinfotech • Windows 10 & Windows 11 help for humans |language=en-US}}</ref>

===Samba Server===
[[Samba (software)|Samba]] on Linux is capable of providing Shadow Copy Service on an [[Logical Volume Manager (Linux)|LVM]]-backed storage or with an underlying [[ZFS]] or [[btrfs]].<ref>{{cite web |url=http://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/VFS.html | title=Samba HOWTO Collection, Part III. Advanced Configuration | access-date=2 October 2012 }}</ref><ref>{{cite web|url=https://github.com/zfsonlinux/zfs-auto-snapshot/wiki/Samba|title=zfsonlinux/zfs-auto-snapshot|website=GitHub|access-date=18 March 2018}}</ref><ref>{{cite web|url=https://forum.openmediavault.org/index.php/Thread/7331-GUIDE-Windows-Previous-Versions-and-Samba-Btrfs-Atomic-COW-Volume-Shadow-Copy/|title=[GUIDE] Windows Previous Versions and Samba (Btrfs - Atomic COW - Volume Shadow Copy)|website=openmediavault}}</ref>

==Compatibility==
While the different [[NTFS]] versions have a certain degree of both [[Forward compatibility|forward]] and [[backward compatibility]], there are certain issues when mounting newer NTFS volumes containing persistent shadow copies in older versions of Windows. This affects dual-booting, and external portable hard drives. Specifically, the persistent shadow copies created by Windows Vista on an NTFS volume are deleted when Windows XP or Windows Server 2003 mount that NTFS volume. This happens because the older operating system does not understand the newer format of persistent shadow copies.<ref>{{cite web | url=http://blogs.technet.com/filecab/archive/2006/07/14/441829.aspx | title=How restore points and other recovery features in Windows Vista are affected when you dual-boot with Windows XP | date=14 July 2006 | work=File Cabinet Blog | publisher=[[Microsoft]] | access-date=21 March 2007 | archive-date=18 July 2006 | archive-url=https://web.archive.org/web/20060718011852/http://blogs.technet.com/filecab/archive/2006/07/14/441829.aspx | url-status=dead }}</ref> Likewise, System Restore snapshots created by Windows 8 are deleted if they are exposed to a previous version of Windows.<ref>{{cite web |url=https://msdn.microsoft.com/en-us/library/windows/desktop/aa378727.aspx | title=Calling SRSetRestorePoint | work = [[MSDN Library]] |publisher=[[Microsoft]] | quote=Snapshots of the boot volume created by System Restore running on Windows 8 may be deleted if the snapshot is subsequently exposed by an earlier version of Windows. | access-date=1 February 2015 }}</ref>

==See also==
{{Wikibooks|Guide to Windows Commands}}
* [[List of Microsoft Windows components]]
* [[Snapshot (computer storage)]]
* [[Copy-on-write]]

==References==
{{Reflist|30em}}

==Further reading==
{{Refbegin}}
*{{cite book
| title     = Windows Internals
| edition   = 5th
| last1     = Russinovich | first1 = Mark E.  | author-link = Mark Russinovich
| last2     = Solomon     | first2 = David A.
| last3     = Ionescu     | first3 = Alex
| publisher = Microsoft Press
| year      = 2009
| chapter   = Storage Management
| pages     = 688–698
| isbn      = 978-0-7356-2530-3
}}
* {{cite web
|url=https://technet.microsoft.com/en-us/library/cc749185(WS.10).aspx
|title=Selected Scenarios for Maintaining Data Integrity with Windows Vista
|work=Microsoft TechNet
|publisher=Microsoft Corporation
|access-date=4 January 2011
}}
* {{cite web
|last1=Russinovich
|first1=Mark
|author-link=Mark Russinovich
|last2=Solomon
|first2=David
|title=Windows XP: Kernel Improvements Create a More Robust, Powerful, and Scalable OS
|url=http://msdn.microsoft.com/en-us/magazine/cc302206.aspx
|work=TechNet Magazine
|publisher=Microsoft
|access-date=2 May 2013
|date=December 2001
}}
* {{cite web
|url=http://blogs.msdn.com/adioltean/archive/2006/09/18/761515.aspx
|title=A bit of black magic: How to assign drive letters to VSS shadow copies... on Windows XP!
|work=Antimail
|publisher=Microsoft Corporation
|first1=Adi
|last1=Oltean
|date=19 September 2006
|access-date=4 January 2011
}}
* {{cite web
|url=http://blogs.msdn.com/adioltean/archive/2004/12/14/301868.aspx
|title=Creating shadow copies from the commandline
|work=MSDN Blogs
|publisher=Microsoft Corporation
|first1=Adi
|last1=Oltean
|date=14 December 2004
|access-date=4 January 2011
}}
* {{cite web
|url=http://blogs.technet.com/b/filecab/archive/2009/06/17/volume-shadow-copy-service-vss-express-writers.aspx
|title=Volume Shadow Copy Service (VSS) Express Writers 
|publisher=Microsoft Corporation
}}
{{Refend}}

{{Windows Components}}
{{Windows commands}}

[[Category:Windows services]]
[[Category:Windows administration]]