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| service_name = VSS〔 | service_description= Volume Shadow Copy | included_with = | also_available_for = Windows 2000, Windows XP RTM or SP1 | related_components = Backup and Restore, File History }} Shadow Copy (also known as Volume Snapshot Service,〔 Volume Shadow Copy Service〔 or VSS〔) is a technology included in Microsoft Windows that allows taking manual or automatic backup copies or snapshots of computer files or volumes, even when 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 the file system to be NTFS 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 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 locked while the backup is being made. The core component of shadow copy is the Volume Shadow Copy 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 can register them with Volume Shadow Copy service. Each provider has a maximum of 10 seconds time to complete the snapshot generation. 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 do not receive acknowledgement of success from the corresponding writers with this time-frame, it fails the operation.〔 By default, snapshots are temporary; they do not survive a reboot. The ability to create persistent snapshots was added in Windows Server 2003 onward. However, Windows 8 removed the GUI portion necessary to browse them. (See ) Windows software and services that support VSS include Windows Backup, Hyper-V, Virtual Server, Active Directory, SQL Server, Exchange Server and SharePoint. 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 VMS) implicitly save a version of files each time they are changed; systems using a snapshotting approach like Windows only capture the state periodically. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shadow Copy」の詳細全文を読む スポンサード リンク
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