Live Recovery of Virtual Machines for Hyper-V


Live recovery quickly restores and starts a VM, before the full restore completes. Live recovery is especially useful when you need to quickly put a failed VM back into production, and when you need to validate that a backup is usable for disaster recovery.


  • You can perform live recovery operations using streaming backups and backup copies.

  • Live Recovery uses a 3DFS cache on the MediaAgent that performs the Live Recovery. By default, the 3DFS cache is located in the Job Results folder for the MediaAgent, but you can change the path using the s3dfsRootDir additional setting. The 3DFS cache is circular, so unused data are pruned from the cache.

Live Recovery Process

Data is restored from the backup as needed to enable the operations requested by the VM, and the full restore completes as resources allow. The backup is not modified by the restore process.

The process for a Live Recovery is:

  1. The 3DFS server (VSA proxy) creates the UNC path, which contains the VHDX file and configuration file.

  2. The 3DFS server registers the UNC path with the Callback File System (CBFS).

  3. The 3DFS server fetches disk related information from indexing, and then, creates disks on the UNC path. (Disk data is restored on demand.)

  4. The 3DFS server fetches the network information, and then, creates the new network.

  5. The VM is imported.

  6. The VM is powered on (unless otherwise indicated by user input).

  7. Read and write request will be passed to the 3DFS server layer through the CBFS.

  8. Complete user specified wait period before relocation.

  9. Move or relocate the storage from the 3dfs cache to the VM.

    During relocation, if there are any writes on the VM, it is managed by the Hyper-V Virtual Machine Management service (VMMS). The service redirects writes to the 3DFS datastore or the destination datastore.

  10. After relocation completes, the 3DFS share is removed, and the UNC path is unregistered from CBFS.