VMware VADP backup set application aware VSS support (for Windows virtual machines)
Creation Date: May 31, 2013
Revision Date: May 31, 2013
Product: DS‑Client (Linux and Windows)
Summary
This article applies to VMware VADP backup sets, when the target virtual machine is running a Windows operating system.
See Also
Volume Shadow Copy Service quiescing
DS-Client uses Microsoft Windows Volume Shadow Copy Service (VSS) quiescing, which provides the backup infrastructure for certain Windows operating systems, as well as a mechanism for creating consistent point-in-time copies of data known as shadow copies.
VSS produces consistent shadow copies by coordinating with business applications, file-system services, backup applications, fast-recovery solutions, and storage hardware. VSS support is provided with VMware Tools, which runs in the guest operating system. VMware provides a VSS Requestor and a VSS Snapshot Provider (VSP).
The requester component is available inside a supported guest and responds to events from DS-Client which connects to VMware using VADP and VDDK APIs. The requester is instantiated by the VMware Tools service when a backup process is initialized. The VSP is registered as a Windows service and notifies the ESXi host when the applications are quiesced so it can take a snapshot of the virtual machine.
VMware Tools uses different quiescing mechanisms depending on the guest operating system that you run in your virtual machines.
Driver type and quiescing mechanisms used according to guest operating systems
Guest operating system: Windows Vista 32-bit/64-bit, Windows 7 32-bit/64-bit |
Driver Type Used | VMware VSS component |
Quiescing Type Used | File-system consistent quiescing |
Guest operating system: On pre-ESX 4.1 Hosts: Windows 2008 32-bit/64-bit, Windows 2008 R2 |
Driver Type Used | VMware VSS component |
Quiescing Type Used | File-system consistent quiescing |
Guest operating system: On ESX 4.1 and later Hosts: Windows 2008 32-bit/64-bit, Windows 2008 R2 |
Driver Type Used | VMware VSS component |
Quiescing Type Used | Application-consistent quiescing. For application-consistent quiescing to be available, three conditions must be met: 1) The UUID attribute must be enabled. This is enabled by default on virtual machines created on ESX 4.1 and later hosts. For virtual machines created on other hosts, complete the procedure Enable Windows 2008 Virtual Machine Application Consistent Quiescing. 2) The virtual machine must use only SCSI disks. For example, application-consistent quiescing is not supported for virtual machines with IDE disks. There must as many free SCSI slots in the virtual machine as the number of disks. For example, if there are 8 SCSI disks on SCSI adapter 1, there are not enough SCSI slots free to perform application quiescing. 3) The virtual machine must not use dynamic disks. |
Guest operating system: Other guest operating systems |
Driver Type Used: | Not applicable |
Quiescing Type Used: | Crash-consistent quiescing |
Additional details
• Application consistent quiescing of Windows 2008 virtual machines is only available when those virtual machines are created in vSphere 4.1 and later.
• Virtual machines created in vSphere 4.0 can be updated to enable application consistent quiescing, Please contact VMware.
• Because VMware Tools uses VSS, DS-Client can create snapshots while ensuring application consistency. This means that applications write to disk any important data that is currently in memory, making sure that a later restore of that virtual machine can restore the application back into a consistent state.
• Detailed information about VSS can be found at http://technet.microsoft.com/en-us/library/cc785914.aspx
In most cases, the quiescing mechanisms provided with VMware Tools will properly quiesce applications. If your environment includes applications or operating systems that do not respond to included quiescing mechanisms as expected, VMware Tools supports the use of custom quiescing scripts. Deploy and run the custom quiescing scripts inside the protected virtual machine.
Locations of custom quiescing scripts
Guest operating system: Windows All scripts are invoked in ascending alphabetical order with freeze as the first argument. |
Script | Pre-freeze |
Location of script on virtual machine | C:\Program Files\VMware\VMwareTools\backupScripts.d |
Guest operating system: Windows All scripts are invoked in descending alphabetical order with thaw or freezeFail as the first argument. |
Script | Post-freeze |
Location of script on virtual machine | C:\Program Files\VMware\VMwareTools\backupScripts.d |
Guest operating system: Other |
Script | Pre-freeze |
Location of script on virtual machine | /usr/sbin/pre-freeze-script |
Guest operating system: Other |
Script | Post-freeze |
Location of script on virtual machine | /usr/sbin/post-thaw-script |
• When running the scripts, you can also use the SYNC driver or VSS components on those virtual machines that support them.
• For more information, contact VMware or Microsoft accordingly
• For further information, see VMware Knowledge Base (#1031298): “Cannot take a quiesced snapshot of Windows 2008 R2 virtual machine”.