A temporary snapshot of the VM is taken and then removed during every backup or replication job session. To remove the snapshot, Veeam Backup & Replication triggers the VMware snapshot consolidation mechanism that includes two steps:
- VMware vSphere removes the snapshot from the VM snapshots list.
- VMware vSphere consolidates the data written to the delta file with the VM disks.
The problem occurs when the snapshot was removed successfully but the consolidation failed. This may happen, for example, if the files appear to be locked when VMware vSphere attempts to consolidate the snapshot files. In this case, the files remain on datastore.
The Snapshot Hunter is started as a separate process scheduled within every job session. The discovery of the phantom snapshots does not affect the job: if the phantom snapshots are discovered, the Veeam Backup Service schedules the snapshot consolidation, and the job runs in normal way.
Veeam Backup & Replication checks the datastore to discover orphaned snapshot files. To consolidate these files with the VM disks, Veeam Backup & Replication calls a consolidation algorithm. The algorithm consists of three steps, each representing a VMware method.
- VMware Consolidate method
As a first attempt, Veeam Backup & Replication calls the VMware Snapshot Consolidate method. This method is the same mechanism that VMware vSphere uses for VMs with the Needs Consolidation status.
- Hard consolidation without quiesce
If the first attempt fails, Veeam Backup & Replication creates a new snapshot and calls the VMware Delete all snapshots method. As a result, all VM snapshots and associated files are deleted. The snapshot is taken without quiescing the VM.
- Hard consolidation with quiesce
If the snapshot deletion still fails, Veeam Backup & Replication implies another VMware method that creates a quiesced snapshot and then removes all VM snapshots.
Hard consolidation without quiesce and hard consolidation with quiesce are performed only if the VM does not have any user snapshots. In case there are one or more user snapshots, these steps will not be performed.
The 3-steps consolidation procedure is launched up to 4 times with a 4-hour interval.
In case all four attempts fail, Veeam Backup & Replication sends an e-mail notification informing that the user needs to manually troubleshoot the problem. Note that you need to have the global email notifications option enabled. For more information, see Specifying Email Notification Settings.
The Snapshot Hunter considers the backup window set for the job. If any of the attempts does not fit the backup window, Veeam Backup & Replication will not perform the consolidation and send the e-mail notification.
You can view information on the Snapshot Hunter sessions on the History > System view in the Veeam Backup & Replication console.
In case no consolidation attempt could fit the backup window, the warning appears in the job statistics.