When you back up or replicate a running VM, you need to quiesce or ‘freeze’ the VM to bring its file system and application data to a consistent state. Data quiescence is crucial for highly-transactional applications. It helps create transactionally consistent backups or replicas and guarantee safety of application data.
To create consistent backups and replicas for VMs that do not support Microsoft VSS (for example, Linux VMs), enable VMware Tools quiescence in job settings. In this case, Veeam Backup & Replication uses the VMware Tools to freeze the file system and application data on a VM before backup or replication.
VMware Tools also allow creating backups and replicas for Microsoft Windows-based VMs that support Microsoft VSS. For this, VMware Tools use VMware VSS component. For details on the supported OSes and quiescence features, see the VMware documentation.
However, to bring applications to a transactionally consistent state before freezing, you must use a pre-freeze script. To bring applications to the initial state after freezing, use a post-freeze script. Store these scripts on the backup server. When a backup or replica job starts, Veeam Backup & Replication uploads these scripts to the appropriate folders on the VM guest OS. For more information, see Pre-Freeze and Post-Thaw Scripts.
By default, VMware Tools quiescence is disabled. You can enable it at the job level. Note that VMware Tools quiescence will be enabled for all VMs added to the job.