Advanced backup options for Hyper-V 2012 R2 on Veeam

Some questions that come up again and again are advanced backup features in Hyper-V using Veeam. How does Veeam take backup from a Hyper-V host?

in a simple day to day virtual machine life, the read & writes consist of I/O traffic from a virtual machines to a VHD/VHDX. Residing on a network share. SAN/SMB and such.

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When we setup Veeam to take backup of a virtual machine, what will happen is the following. First thing is that Veeam will trigger a snapshot using the Hyper-V Integration Services Shadow Copy Provider on that particular Hyper-V host that the virtual machine resides on. What will happen is that a AVHDX. This can either be done using an hardware VSS provier or software VSS provider.

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A hardware provider manages shadow copies at the hardware level by working in conjunction with a hardware storage adapter or controller. A software provider manages shadow copies by intercepting I/O requests at the software level between the file system and the volume manager. The number of VMs in a group is limite depending on VSS provider. For a software VSS provider — 4 VMs, for a hardware VSS provider — 8 VMs.

NOTE: Using Offhost-proxy, requires an storage solution which supports an hardware transferrable shadow copies against a SAN. If we for instance use SMB based storage for Hyper-V we do not require this –> http://helpcenter.veeam.com/backup/hyperv/smb_off-host_backup.html

Using onhost backup, means that the transport role will be using on a Hyper-V host which has access to the running virtual machines.

Make sure that the integration services and running and up to date before doing online backup, you can check this from Hyper-V PowerShell –> Get-VM | FT Name, IntegrationServicesVersion
More troubleshooting on interation services here –> https://www.veeam.com/kb1855

So what will happen in a online backup is (If all the requirements are meet)

1: Veeam will interact with the Hyper-V host VSS service and request backup of the specific VM

2: The VSS writer on the hyper-v host will then forward the reques tto the Hyper-V Integration components inside the VM guest OS

3: The integration components will then communicate with the VSS framework inside the guest OS and request backup of all VSS-aware application inside the VM

4: The VSS writers of application aware VSS will then get application data suiteable for backup

5: After the applications are quiesced the VSS inside the Virtual machine takes an internal snapshot using the software based VSS

6: The integration service component notifices the Hypervisor that the VM is ready for backup, and Hyper-V will then take a snapshot of the volume which the Virtual machine is located on. Then a AVHDX file will be generated, all WRITES will be redirected there.

7: The volume snapshot is presented to Veeam either using Off-host or on-host backup. (If the Off-host proxy is not available it will fallback to on-host proxy on a designeted host)

8: Data will then be processed on the proxy server and then be moved to the repository

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NOTE: Off-host setup requires an dedicated Hyper-V host (It requires Hyper-V to have access to the VSS providers) and in case of using Off-host it cannot be part of the Hyper-V cluster, and make sure it has READ only access to the LUN and that your storage vendors supports readable shadow volume copies.

On-host backup will use the Veeam transport service on the Hyper-V machine. If the volume is placed on a CSV volume, the CSV Software Shadow Copy Provider will be used for the snapshot creation process.

NOTE: During the backup process, Veeam will try to use its own CBT driver on Hyper-V host to make sure that it only takes backup of only the changed blocks. (Since Hyper-V does not natively provide CBT, this will change in Windows Server 2016)

NOTE: If CBT is not working on Veeam run the command Reset-HvVmChangeTracking PowerShell cmdlet http://helpcenter.veeam.com/backup/80/powershell/reset-hvvmchangetracking.html, or if the virtual machines are being shut down during backup process, try to disable ODX)

If Change block tracking is not enabled or not working as it should, the backup proxy will copy the virtual machine and use Veeam’s proprietary filtering mechanism. so Instead of tracking changed blocks of data, Veeam Backup & Replication filters out unchanged data blocks. During backup, Veeam Backup & Replication consolidates virtual disk content, scans through the VM image and calculates a checksum for every data block. Checksums are stored as metadata to backup files next to VM data.

So what about the more advanced features for Hyper-V

Hyper-V Settings

  • Enable Hyper-V guest quiescene

In case of application aware, The VM OS is suspsended and the content of the system memory and CPU is written to a dump file, in order to be able to perserve the data integrity of files with for instance transactional applications (This is known as offline backup)

Note that using this feature Veeam will not be able to perform application tasks like

    • Applying application-specific settings to prepare applications for VSS-aware restore at the next VM startup
    • Truncating transaction logs after successful backup or replication.
  • Take Crach consistent backup instead of suspending VM

If you do not want to suspend the virtual machine during backup, you can use crach consistent backup instead of suspending the virtual machine. This is equal to a hard reset of a virtual machine, this does not involve any downtime to a virtual machine but it does not preserve the data integrity of open files and may result in data loss.

  • Use changed block tracking data

Use the Veeam filter driver to look at changed blocks before data is copied to the offhost-veeam proxy or on-host proxy to the repository

  • Allow Processing of multiple VMs with a single volume snapshot

If you have multiple virtual machines within the same job, this feature will help reduce the load on the Hyper-V hosts.As this will trigger a volume snapshot for mulitple machines instead of a single virtual machine.

NOTE: The virtual machines much be located on the same host and must reside on a file share which uses the same VSS provider.

This is the first post of series – Veeam post and Hyper-V processing.

#backup, #hyper-v, #veeam