Step 1

Virtual machine backup request is initiated based on:

• Schedule defined in the backup policy.
• On-demand backup

Druva forwards the backup request to the agent.

Step 2

Hybrid Workloads agent verifies that the VSS service is running. The Hybrid Workloads agent requests the VSS service to create a snapshot. If the VSS service is not running, Hybrid Workloads agent starts the VSS service and instructs VSS to create a snapshot.

Druva recommends that you enable Backup (volume snapshot) under Hyper-V Integration Services. If the Backup (Volume snapshot) is enabled, the VSS service can create a snapshot without interrupting services on the virtual machine.

Hybrid Workloads agent validates if snapshots are created successfully and initiates the backup job.
For  Windows Server 2008 and Windows Server 2008 R2 host:

• If Druva is backing up virtual machines that are stored on a clustered shared volume, then Druva can backup only one virtual machine at a time. 
• A hardware VSS provider is required if  you want Druva to create snapshots for multiple virtual machines simultaneously on a single host and run parallel backup jobs. For information on how to configure Druva so that it can use third party VSS providers, see How do I configure Druva to use third party VSS providers?.

Note: Integration Services are available for virtual machines with Windows guest OS. However, Microsoft provides Integration Services for certain Linux distributions also. For more information, see:

• Backup (volume snapshot) under Integration Services [External link to Microsoft TechNet article]
• Supported Linux and FreeBSD virtual machines for Hyper-V on Windows [External link to Microsoft TechNet article]

If integration services are not available for a virtual machine, Druva cannot take a snapshot and backup fails.

On Windows Server 2016 or later, the Hybrid Workloads agent can back up virtual machines using the Resilient Change Tracking (RCT) feature if:

• The Hybrid Workloads agent installed on the host is 4.7.5 or later, and
• Virtual machine configuration version is 6.2 or later. If the virtual machine is hosted on a Hyper-V cluster, then the virtual machine cluster functional level must be level 9 or higher. 

The Hybrid Workloads agent can back up virtual machines using RCT on a Hyper-V host that meets the criteria above and:

• Efficiently keep a track of what has changed on a virtual machine between backup jobs
• Incremental backups will be faster

Note: The Hybrid Workloads agent can take virtual machine snapshots using the RCT feature if it is backing up virtual machines for the first time from a host that meets the criteria. The Hybrid Workloads agent continues to use VSS if snapshots of the virtual machines from a host exist that were created using VSS. However, if:

• VSS snapshots exist from a host that meets the criteria above, and
• You want subsequent backup jobs to use the RCT feature   

Upgrade the Hybrid Workloads agent on the host and change backup method to RCT.  

Step 3

Druva determines the type of backup. 

• If this is the first automatic backup, Druva performs a full backup. 
• For all subsequent backups, Druva performs an incremental backup. 

Step 4

Agent estimates the data for backup

Step 5

Agent backs up the data based on the VSS provided snapshot