For restore from backups of Microsoft SQL Server VMs, Veeam Mount Service – a component that is responsible for mount operations – creates an additional mount point on the original VM, and, if necessary, on the staging Microsoft SQL Server. As said, mount to the staging server is used when you perform restore to a specific transaction, or if Veeam Backup & Replication does not have information about databases (for example, if you initiate restore from storage snapshots).
To create a mount point on Microsoft Windows machines, Veeam uses the iSCSI protocol. The remote machine (original VM) or staging server acts as an iSCSI initiator. The mount server associated with the backup repository acts as an iSCSI target. The iSCSI mount point is non-persistent – it is created only for duration of the restore process.