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arcserve-KB : Hyper-V guest VM's are put into a Saved State during Arcserve UDP Agentless Backups.

Last Update: 2016-07-15 02:06:40 UTC
Description:
This document explains about the reason why the Hyper-V guest VM’s would be put into Saved State during UDP Agentless Backups and about the considerations to avoid Saved State Backup.
This also explains about the Hyper-V Snapshot Method options available in UDP and how it works.

Problem:
Hyper-V guest VM's are put into a Saved State during UDP Agentless Backups. When the VM is in Saved State, the VM would be Offline temporarily. This is because the Hyper-V VSS Writer cannot do an Online Backup of this VM.

How can we check this?
We can use the Disk Shadow tool to check this,
https://technet.microsoft.com/en-us/library/cc772172.aspx

Open CMD as Administrator on the Hyper-V Host and run the following commands,

Diskshadow /l vss.log

List writers

Exit

Then open the output file vss.log and search for the VM name under Hyper-V writer.  Check VSS Caption mode for  the VM. If it is set to Saved State that means that from VSS point of view the VM does not support online backup. For example, here is a sample output from a Hyper-V server.

WRITER 'Microsoft Hyper-V VSS Writer'

                                - Writer ID   = {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}

                                - Writer instance ID = {6faa67ee-7239-4393-a9c5-6a8bf90acdd4}

                                - Supports restore events = TRUE

                                - Writer restore conditions = VSS_WRE_ALWAYS

                                - Restore method = VSS_RME_RESTORE_IF_CAN_REPLACE

                                - Requires reboot after restore = FALSE

                                - Excluded files:

                                + Component 'Microsoft Hyper-V VSS Writer:\0F592699-CBF1-404B-BBAB-19944EC9BDD8'

                                                - Name: 0F592699-CBF1-404B-BBAB-19944EC9BDD8

                                                - Logical path: 

                                                - Full path: \0F592699-CBF1-404B-BBAB-19944EC9BDD8

                                                - Caption: Backup Using Saved State\base_win2008R2

If the VM does support online backup then you should see Caption set to Backup Using Child Partition Snapshot.

Details about Hyper-V Snapshot Mechanism and considerations for Online Backup (Child VM Snapshot)
Hyper-V uses one of two mechanisms to back up each VM. The default backup mechanism is called the 'Saved State' method, where the VM is put into a saved state during the processing of the PrepareForSnapshot event, snapshots are taken of the appropriate volumes, and the VM is returned to the previous state during the processing of the PostSnapshot event.

The other backup mechanism is called the 'Child VM Snapshot' method, which uses VSS inside the child VM to participate in the backup. For the 'Child VM Snapshot' method to be supported, all of the following conditions must be met:

  • Backup (volume snapshot) Integration Service is installed and running in the child VM. The service name is 'Hyper-V Volume Shadow Copy Requestor'.
    Windows 2000:  Backup Integration Service is not supported.
  • The child VM must be in the running state.
  • The Snapshot File Location for the VM is set to be the same volume in the host operating system as the VHD files for the VM.
  • All volumes in the child VM are basic disks and there are no dynamic disks.
  • All disks in the child VM must use a file system that supports snapshots (for example, NTFS).
  • The Shadow Copy Storage Area for each volume inside the VM should be associated to its own volume. For example, the Shadow Copy Storage area for volume C:\ should be configured to C:\.
  • There should be 2 GB of space free on VHD inside the Virtual Machine.
  • There should not be any pass through drives and any snapshot(.avhd) being created for the VM.
  • VSS should be working fine on the host and in Virtual Machine as well.
Please refer the following Microsoft Article to understand more about Saved State Snapshots,

https://msdn.microsoft.com/en-us/library/dd405549(VS.85).aspx

If the problem still continues in spite of checking all the considerations, please open a ticket with Microsoft to check on this.

Arcserve UDP provides options to select the Hyper-V Snapshot Method:-

Refer Point 9 in the below mentioned article,

http://documentation.arcserve.com/Arcserve-UDP/Available/V5/ENU/Bookshelf_Files/HTML/Solutions%20Guide/index.htm?toc.htm?caudp_specify_source_hbbu_plan.html

This is available under the Source tab of the Host-Based Agentless Backup Plan.



VM must be backed up using snapshots generated by Microsoft VSS method

Indicates that Arcserve UDP uses the native snapshot methods of Microsoft - online and offline for the backup job. This is the default option. When this checkbox is not selected and when both Microsoft online and offline methods are not available, the backup job uses the Arcserve UDP method to back up the virtual machine.

If the Microsoft offline method is used for backup and the virtual machine is required to be in a Saved state, select the VM may be placed into 'Saved' state before snapshot is taken check box also. If you do not select this check box, the backup job fails. 

Online backup is the recommended backup method because it supports the application consistent backup without the downtime of the virtual machine. The virtual machine is accessible during the backup. The online backup method must satisfy some prerequisites such as integration services must be installed and running. If any of the prerequisites are not satisfied, then only the offline backup method is used. The Microsoft offline backup method has two approaches - save state approach and checkpoint approach. If the Hyper-V host has the Windows 2012R2 operating system with KB 2919355 or later, then the checkpoint approach is used; else the save state approach is used. The major difference between these two approaches is that the save state approach requires the virtual machine to be inaccessible. The virtual machine must be placed into a saved state for a few minutes while taking the snapshot. 

Apart from the Microsoft native snapshot methods, Arcserve UDP has its own snapshot method that can be used when the Microsoft native snapshot methods are not available.

Note: Both Microsoft offline method and Arcserve UDP method are crash consistent backup methods. Both the methods cannot guarantee data integrity. The main difference between the methods is that the Microsoft offline method can be compared to the state that VM has been powered off abruptly whereas the Arcserve UDP method can be compared to the state that Hyper-V host has been powered off abruptly.

VM may be placed into 'Saved' state before snapshot is taken

Indicates that the virtual machine is placed in the Saved state, if required, before taking the VSS snapshot. Select this option when the virtual machine does not support the online backup. If the virtual machine supports the online backup, then even on enabling this option the virtual machine will not be in the Saved state.

Arcserve recommends Snapshot Method in the following order,

1. MS Online Snapshot Method. It is application consistent. If the requirement cannot be met, refer the following section in this article,
'Details about Hyper-V Snapshot Mechanism and considerations for Online Backup (Child VM Snapshot).'

2. MS Offline Snapshot Method. Crash consistent. If VM’s downtime due to saved state is acceptable, use MS Offline Snapshot Method instead of Arcserve Snapshot Method because it brings better consistency.

3. Arcserve Snapshot Method. Crash consistent. There is no downtime of VM.

Windows Logs which would help in analyzing the Snapshot Problem

On the Hyper-V Host, check the following Hyper-V Event Logs:

  • Hyper-V-VMMS: 
    The virtual machine management services files its events in this log.
  • Hyper-V-Worker: 
    The worker process that is used for the actual running of the virtual machine files the events in this log.
On the Hyper-V Guest VM, check the following Event Logs:

  • Windows System Event Log
  • Windows Application Event Log
  • Output of vssadmin list writers, vssadmin list providers, vssadmin list shadowstorage
 
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