Working with Microsoft
Shadow CopyLast Updated December 16, 2024
Microsoft Shadow Copy, also called Volume
Snapshot Service (VSS), is a Windows Server data backup feature for creating
consistent point-in-time copies of data (called shadow copies).
The type of quiescing used varies depending on the
operating system of the backed-up virtual machine, as shown in
Table 1.
ESXi 4.1 added support for Windows 2008 guests using application level
quiescing.
Guest Operating System | Driver Type Used | Quiescing Type Used |
---|---|---|
Windows XP 32-bit Windows 2000 32-bit | Sync Driver | File-system consistent quiescing.
|
Windows Vista 32- or 64-bit Windows 7 32- or 64-bit | VMware VSS component | File-system consistent quiescing.
|
Windows 2003 32- or 64-bit | VMware VSS component | Application-consistent quiescing.
|
Windows 2008 32- or 64-bit Windows Server 2008 R2 | VMware VSS component | Application-consistent quiescing.
For this to be available, several conditions must be met:
|
Windows Server 2012 | VMware VSS component | Same as for Windows 2008. |
Windows Server 2016 | VMware VSS component | Same as for Windows 2008. VMware Tools 10.1.0 or later is required for quiescing support.
Application quiesced
snapshots are not supported for encrypted VMs, nor for virtual disks
managed by Storage Spaces. Use file-system quiescing instead.
|
Windows Server 2019 | VMware VSS component | Same as for Windows 2016. |
Windows Server 2022 | VMware VSS component | Same as for Windows 2016. |
Other guest operating system | Not applicable | Crash-consistent quiescing.
|
File-system consistent quiescing prevents file
systems from becoming corrupted, for example, journaled file systems are
allowed to write out pending transactions. Crash-consistent quiescing is the
ability to restore an application as if it suddenly crashed and lost all
stateful information. This involves minimal effort because only data already
written to disk is guaranteed safe. Application-consistent quiescing is the
ability to restore stateful information as well.
Restore must be done using the backup
application’s guest agent. The vSphere APIs for Data Protection provide no host
agent support for this. Applications authenticating with SSPI might not work
right because HTTP access will demand a user name and password, unless the
session was recently authenticated.
When performing VSS quiescing while creating the
snapshot of a Windows virtual machine, VMware Tools generate a
vss-manifest.zip
file
containing the backup components document (BCD) and writer manifests. The host
agent stores this manifest file in the
snapshotDir
of the virtual
machine. Backup applications should get the
vss-manifest.zip
file so they
can save it to backup media. There are several ways to get this file:
- Using the datastore access HTTPS protocol, for example by browsing to https://<server-or-host>/folder/ and continuing downward to the snapshot directory until you find thevss-manifest.zipfile.
- By calling theCopyDatastoreFile_Taskmethod in the vSphere API. This method accepts the URL formulated above for HTTPS, or a datastore path. (CopyVirtualDisk_Taskis for VMDK files).
- With thevifscommand in the vMA or vCLI.
- With theCopy-DatastoreItemcmdlet in the PowerCLI (requires PowerShell and VMware snap-in).
Windows 2008 application level quiescing is
performed using a hardware snapshot provider. After quiescing the virtual
machine, the hardware snapshot provider creates two redo logs per disk: one for
the live virtual machine writes and another for the VSS and writers in the
guest to modify the disks after the snapshot operation as part of the quiescing
operations.
The snapshot configuration information reports
this second redo log as part of the snapshot. This redo log represented the
quiesced state of all the applications in the guest. This redo log must be
opened for backup with VDDK 1.2 or later. The older VDDK 1.1 software cannot
open the second redo log for backup.
Application consistent quiescing of Windows 2008
virtual machines is only available when those virtual machines are created in
vSphere 4.1 or later. Virtual machines created in vSphere 4.0 can be updated to
enable application consistent quiescing by modifying a virtual machine’s
enableUUID attribute.
For information about VSS, see the Microsoft
TechNet article,
How Volume Shadow Copy Service Works
.
For information about Security Support Provider Interface (SSPI), see the MSDN
Web site.