62847: Acronis Backup: Troubleshooting Hyper-V snapshot issues

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    This article applies to backups of Hyper-V VMs performed by Agent for Hyper-V (agent-less)

    About 

    Prerequisites

    Prior to performing the backup, make sure that the below prerequisites are met:

    1. Hyper-V Integration Services must be up-to-date and running inside the virtual machine(s).

    2. In order to avoid VM going into "saved" state during backup, make sure that the Integration services -> Backup (Volume checkpoint) option is enabled in VM settings in Hyper-V Manager.

    3. For application-aware backup: there must be network connection from Agent for Hyper-V to guest VM network, since application data is read over WMI which requires network connection to guest OS.

    4. For application-aware backup: there must be no Windows dynamic disks present in the guest OS.

    Snapshot creation

    Hyper-V 2012 R2 or lower: The Agent for Hyper-V acts as a VSS requestor to create a VSS snapshot of the Hyper-V host volume, where the virtual disks of the backed up VM reside (could be CSV or SMB3), via VSS service on the Hyper-V host. VSS service uses the Hyper-V VSS writer to quiesce the guest operating system via the Hyper-V Integration Services installed in the guest OS during the VSS snapshot of the host volume. The virtual disks of the backed up VM are accessed (opened for Read operation) within the created VSS snapshot of the host volume.

    See this Technet article describing Planning for Backup of the Hyper-V virtualization environment for more information. See the Technet article about Volume Copy Shadow Service technology.

    Note that VSS snapshot is not the same as the Hyper-V Virtual Machine snapshot (checkpoint). The latter is not used as data source for VM backup - it is used to quiesce guest OS of the VM.

    Hyper-V 2016 or higher: On Windows Hyper-V Server 2016 or newer there is a new Microsoft Resilient Change Tracking (RCT) API used to capture/track the VM data, which is read directly from VM-level snapshot (checkpoint). See details here.

    VM data backup

    The Agent for Hyper-V reads the data from the virtual disks files within the created snapshot (VSS snapshot or VM-level snapshot) along with VM configuration and copies the data blocks into the .tib(x) file.

    Recommended setup

    To avoid conflicts by snapshot creation, it is not recommended to back up physical host and virtual machines in the same backup plan on a permanent basis.

    Known issues

    If you are backing up Hyper-V VM with Linux guest OS installed in it, you may receive a warning "Cannot create application-consistent snapshot" which is the result of failure to create "production" checkpoint on Hyper-V level and Acronis Backup automatically fails over to non-production checkpoints (crash-consistent backup) after 3 (by default) unsuccessful attempts to trigger "production" checkpoint. To fix this issue you should either troubleshoot "production" checkpoint failure for particular VM (described in Troubleshooting section below) OR as a workaround go to backup plan options and disable the option Volume Shadow Copy Service (VSS) for virtual machines. Note that disabling this option would capture the guest OS in crash-consistent state.

    Troubleshooting

    If all prerequisites are met but backup still fails with a snapshot-related error, test snapshot creation with the native Windows tools

    Hyper-V 2012 R2 or lower

    Verify whether it is possible to successfully backup the VM using Windows Server Backup.

    To backup a VM with Windows Server Backup, run the following command in Command Prompt on Hyper-V Server:

    wbadmin start backup -backuptarget:<location>: -hyperv:<VM_name>

    where <location> is the backup destination and <VM_name> is the name, e.g. wbadmin start backup -backuptarget:\\Server\share: -hyperv:VM01 

    If backup with Windows Server backup fails, collect the output of Windows Server Backup operation as well as the diagnostic information described below and contact Acronis Customer Central.

    If backup with Windows Server is successful but backup operations in Acronis Backup still fails, collect the diagnostic information described below and contact Acronis Customer Central.

    Hyper-V 2016 or higher

    Verify whether it is possible to create a production checkpoint of this VM.

    In Hyper-V Manager open this VM settings, go to Management -> Checkpoints, and select Enable Checkpoints, then Production Checkpoints and unselect the checkbox Create standard checkpoints if it's not possible to create production checkpoint.

    After specifying these options, try to create a checkpoint of this virtual machine via Hyper-V Manager.

    If creating a checkpoint fails, investigate the issue with the VM by analyzing the Hyper-V logs in Windows Event Viewer. Acronis Backup relies on successful snapshot (checkpoint) creation for capturing data for backup.

    If checkpoint is created successfully but backup still fails, collect the diagnostic information described below and contact Acronis Customer Central.

    Collect information

    1) System information from the affected server

    • Acronis Backup 12.5: click here
    • Acronis Backup Cloud: click here

    2) Logs with information about VM checkpoints operations and failures related to Hyper-V VMs snapshots/checkpoint creation failure.

    On Hyper-V server, open Windows Event Viewer (press Win+R to open the Run dialog, enter eventvwr.msc and hit OK). You need the following logs:

    • Event Viewer > Applications and Services Logs > Microsoft > Windows > Hyper-V worker -> Admin
    • Event Viewer > Applications and Services Logs > Microsoft > Windows > Hyper-V-VMMS > Admin + Operational

    Right-click on the log and select Save all events as, and save the log as .evtx file

    3) For Windows guest OS: collect Windows Event logs related to VSS.

    In guest OS, open Windows Event Viewer (press Win+R to open the Run dialog, enter eventvwr.msc and hit OK). You need the following logs:

    • Event Viewer > Windows Logs > Application
    • Event Viewer > Windows Logs > System

    Right-click on the log and select Save all events as, and save the log as .evtx file

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