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VSS_SNAPSHOT_CONTEXT enumeration (vss.h)

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The _VSS_SNAPSHOT_CONTEXT enumeration enables a requester using IVssBackupComponents::SetContext to specify how a shadow copy is to be created, queried, or deleted and the degree of writer involvement.

Syntax

typedef enum _VSS_SNAPSHOT_CONTEXT {
  VSS_CTX_BACKUP = 0,
  VSS_CTX_FILE_SHARE_BACKUP,
  VSS_CTX_NAS_ROLLBACK,
  VSS_CTX_APP_ROLLBACK,
  VSS_CTX_CLIENT_ACCESSIBLE,
  VSS_CTX_CLIENT_ACCESSIBLE_WRITERS,
  VSS_CTX_ALL = 0xffffffff
} VSS_SNAPSHOT_CONTEXT, *PVSS_SNAPSHOT_CONTEXT;

Constants

 
VSS_CTX_BACKUP
Value: 0
The standard backup context. Specifies an auto-release, nonpersistent shadow copy in which writers are
involved in the creation.
VSS_CTX_FILE_SHARE_BACKUP
Specifies an auto-release, nonpersistent shadow copy created without writer involvement.
VSS_CTX_NAS_ROLLBACK
Specifies a persistent, non-auto-release shadow copy without writer involvement. This context should be
used when there is no need for writer involvement to ensure that files are in a consistent state at the time
of the shadow copy.


Lightweight automated file rollback mechanisms or persistent shadow copies of file shares or data volumes
that are not expected to contain any system-related files or databases might run under this context. For
example, a requester could use this context for creating a shadow copy of a NAS volume hosting documents and
simple user shares. Those types of data do not need writer involvement to create a consistent shadow copy.
VSS_CTX_APP_ROLLBACK
Specifies a persistent, non-auto-release shadow copy with writer involvement. This context is designed
to be used when writers are needed to ensure that files are in a well-defined state prior to shadow copy.


Automated file rollback mechanisms of system volumes and shadow copies to be used in data mining or restore
operations might run under this context. This context is similar to VSS_CTX_BACKUP
but allows a requester more control over the persistence of the shadow copy.
VSS_CTX_CLIENT_ACCESSIBLE
Specifies a read-only, client-accessible shadow copy that supports Shadow Copies for Shared Folders and is created without writer involvement. Only the system provider (the default provider available on the system) can create this type of shadow copy.

Most requesters will want to use the VSS_CTX_NAS_ROLLBACK context for persistent, non-auto-release shadow copies without writer involvement.
VSS_CTX_CLIENT_ACCESSIBLE_WRITERS
Specifies a read-only, client-accessible shadow copy that is created with writer involvement. Only the system provider (the default provider available on the system) can create this type of shadow copy.

Most requesters will want to use the VSS_CTX_APP_ROLLBACK context for persistent, non-auto-release shadow copies with writer involvement.

Windows Server 2003 and Windows XP:  This context is not supported by Windows Server 2003 and Windows XP.
VSS_CTX_ALL
Value: 0xffffffff
All types of currently live shadow copies are available for administrative operations, such as shadow copy
queries (see IVssBackupComponents::Query).
VSS_CTX_ALL is a valid context for all VSS interfaces except
IVssBackupComponents::StartSnapshotSet
and
IVssBackupComponents::DoSnapshotSet.

Remarks

The data type to be used with values of _VSS_SNAPSHOT_CONTEXT is LONG.

The default context for VSS shadow copies is VSS_CTX_BACKUP.

Windows XP:  The only supported context is the default, VSS_CTX_BACKUP. Calling IVssBackupComponents::SetContext will return E_NOTIMPL.

For details on how to use VSS shadow copies contexts, see Implementation Details for Creating Shadow Copies.

Shadow copy behavior can be further controlled by using a bitwise OR to combine a supported _VSS_VOLUME_SNAPSHOT_ATTRIBUTES with valid _VSS_SNAPSHOT_CONTEXT values as an argument to the IVssBackupComponents::SetContext method.

Currently, the only supported modifications are the bitwise OR of a _VSS_SNAPSHOT_CONTEXT value with the VSS_VOLSNAP_ATTR_TRANSPORTABLE and either the VSS_VOLSNAP_ATTR_DIFFERENTIAL or the VSS_VOLSNAP_ATTR_PLEX value of the _VSS_VOLUME_SNAPSHOT_ATTRIBUTES enumeration.

However, these values cannot be used to modify VSS_CTX_CLIENT_ACCESSIBLE context.

The use of VSS_VOLSNAP_ATTR_TRANSPORTABLE is limited to systems running Windows Server 2008 Enterprise, Windows Server 2008 Datacenter, Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition.

Requirements

Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header vss.h

See also

IVssBackupComponents::DoSnapshotSet

IVssBackupComponents::ExposeSnapshot

IVssBackupComponents::SetContext

VSS_OBJECT_PROP

VSS_SNAPSHOT_PROP

_VSS_VOLUME_SNAPSHOT_ATTRIBUTES