For backup and replication of VMs that reside on SMB3 shares, Veeam Backup & Replication uses a native Hyper-V approach leveraging the Microsoft VSS framework. Veeam Backup & Replication acts as a VSS requestor: it communicates with the VSS framework and triggers a shadow copy of the necessary file share. The Microsoft VSS components create a file share shadow copy and present it to Veeam Backup & Replication, which uses the shadow copy for backup.
To properly quiesce VMs on SMB3 shares, Hyper-V uses three VSS frameworks. These frameworks work at the level of the Hyper-V host and at the level of the SMB3 file server and communicate with each other:
1. VSS framework on the Hyper-V host (Hyper-V host VSS). When Veeam Backup &
Replication starts the backup process, it communicates directly with the VSS framework on the Hyper-V host where the VM is registered. The Hyper-V host VSS service initiates creation of the file share shadow copy, freezes VM application writes and passes the request for shadow copy to the VSS for SMB File Shares framework. After the shadow copy is created, the Hyper-V host VSS service returns a path to the shadow copy to Veeam Backup & Replication.
VSS for SMB File Shares. This framework is Microsoft’s extension to its VSS framework.
VSS for SMB File Shares provides application-consistent shadow copies of VMs on SMB3 network shares. To work with shadow copies of file shares, VSS for SMB File Shares uses two components:
File Share Shadow Copy Provider is a VSS provider for SMB3. The File Share Shadow Copy Provider is invoked on the Hyper-V host where the VM is registered. The provider uses VSS APIs to interact with the VSS requestor, File Share Shadow Copy Agent, and request creation of file shares shadow copies.
File Share Shadow Copy Agent is a VSS requestor for SMB3. The File Share Shadow Copy Agent is invoked on the SMB3 file server. The agent interacts with the local VSS framework on the SMB3 file server to create a shadow copy of the requested file share.
2. Local VSS framework on the SMB3 file server. This framework is responsible creating a shadow copy of the volume on which the file share is located and exposing the shadow copy as a file share on the SMB3 server.
Backup of VMs on SMB3 shares includes the following steps:
1. Veeam Backup & Replication interacts with the Hyper-V host VSS Service and requests a shadow copy of the necessary file share.
2. The Hyper-V host VSS Service sends a request to prepare a shadow copy to the Hyper-V host VSS Writer. The Hyper-V host VSS Writer flushes buffers and holds application writes on VMs.
3. The Hyper-V host VSS Service sends a request for shadow copy creation to the File Share Shadow Copy Provider invoked on the Hyper-V host.
4. The File Share Shadow Copy Provider relays the request to the File Share Shadow Copy Agent invoked on the SMB3 file server hosting the necessary file share.
5. The File Share Shadow Copy Agent triggers a request for shadow copy creation to the local VSS Service on the SMB3 file server.
6. The local VSS Service on the SMB3 file server uses the necessary shadow copy provider to create a shadow copy of the volume on which the necessary file share is located. The shadow copy is exposed as a file share on the SMB3 server. After that, application writes on VMs located on the original file share are resumed.
7. The File Share Shadow Copy Agent returns a path to the shadow copy to the File Share Shadow Copy Provider.
8. The File Share Shadow Copy Provider communicates this information to the Hyper-V host VSS Service.
9. Veeam Backup & Replication retrieves information about the shadow copy properties from the Hyper-V host VSS Service.
10. Veeam Backup & Replication uses the created shadow copy for backup. After backup is complete, the file share shadow copy is destroyed.
Backup Modes
For backup and replication of VMs on SMB3 shares, you can use onhost backup and offhost backup.
Onhost Backup
Onhost backup of VMs on SMB3 shares is similar to onhost backup of VMs on local storage and CSV. During onhost backup, the Hyper-V VSS components, File Share Shadow Copy Provider and Veeam agent are invoked on the source Hyper-V VSS host. The File Share Shadow Copy Agent is invoked on the SMB3 server. As a result, all data processing is accomplished directly on the source Hyper-V host and on the SMB3 server.
The onhost backup process includes the following steps:
1. Veeam Backup & Replication triggers a shadow copy of the necessary file share. Microsoft VSS components invoked on the Hyper-V host and SMB3 server create a shadow copy of the volume on which the requested file share is located and expose the shadow copy as a file share on the SMB3 server.
2. The Veeam agent deployed on the Hyper-V host accesses the shadow copy file share exposed on the SMB3 server. Veeam Backup & Replication retrieves VM data from the shadow copy, processes the data and copies it to the destination.
3. Once the backup process is complete, the shadow copy is deleted.
Offhost Backup
In general, the main concept of offhost backup for VMs on SMB3 shares is similar to offhost backup of VMs on local storage or CSV. During offhost backup, the Hyper-V VSS processing operations are shifted from the source V host to a dedicated machine — offhost backup proxy. The Hyper-V Hyper-VSS components, File Share Shadow Copy Provider and Hyper-Veeam agent are invoked on the offhost backup proxy, instead of the source Hyper-V host. The File Share Shadow Copy Agent is invoked on the SMB3 server. As a result, all data processing is accomplished on the offhost backup proxy and SMB3 server; the source Hyper-V host remains unaffected.
To be able to perform offhost backup, you must meet the following requirements:
1. You must configure an offhost backup proxy. The role of an offhost backup proxy can be assigned only to a Microsoft Windows 2008 Server R2 machine with the Hyper-V role enabled or to a Microsoft 2012 machine with the Hyper-V role enabled.
2. In the properties of a backup or replication job, you must select the offhost backup method. If necessary, you can assign the job to a specific proxy. To learn more, see the Configuring Advanced Options for Offhost Backup Proxies section.
3. The Local System account of the offhost backup proxy must have full access permissions on the SMB3 file share.
4. The offhost backup proxy should be located in the same domain where the SMB3 server resides. Alternatively, the domain where the SMB3 server resides should be trusted by the domain in which the offhost backup proxy is located.
The offhost backup process includes the following steps:
1. Veeam Backup & Replication triggers a shadow copy of the necessary file share. Microsoft VSS components invoked on the offhost backup proxy and SMB3 server create a shadow copy of the volume on which the requested file share is located and expose the shadow copy as a file share on the SMB3 server.
2. The Veeam agent on the offhost backup proxy accesses the shadow copy on the SMB3 server. It retrieves VM data from the shadow copy, processes the VM data and copies it to the destination.
3. Once the backup process is complete, the shadow copy is deleted.