Job efficiency and time required for its completion are highly dependent on the data transport mode. Transport mode is a method used by the Veeam proxy to retrieve VM data from the source host and write VM data to the target destination.
In this mode, the backup proxy server has direct access to the storage volumes on which VMs reside. When configured, the backup proxy will retrieve data directly from the storage, bypassing the ESXi infrastructure.
Depending on storage protocols utilized, the proxy can be deployed as follows:
On a physical server for FibreChannel, FCoE, iSCSI or NFS
On a virtual machine for iSCSI and NFS
As the disks are hot-added, you may find the virtual appliance mode referred to as
hotadd in documentation and logs.
To work in this mode the backup proxy must be deployed as a VM. For smaller deployments (e.g., several branch offices with a single ESXi host per each office) you can deploy a virtual backup proxy on a ESXi host that has access to all required datastores. When backup or replication takes place and a VM snapshot is processed the snapshotted disks are mapped to the proxy to read data (at backup) and write data (at restore/replication); later they are unmapped.
You may find network mode referred to as
nbd in documentation and logs.
The most widespread backup method is network mode, which transports VM data through the VMkernel interfaces of the VMware ESXi host on which the VM resides.
The benefit of using NBD is the fact that it requires no additional configuration, and is supported regardless of physical or virtual proxy deployments, or storage protocols used (including local storage, VMware Virtual Volumes or VMware vSAN). This is also the reason NBD is used as the fallback method, in case Backup from Storage Snapshots, Direct Storage Access or Virtual Appliance backup modes fail.
The only requirement is for the proxy to be able to access ESXi hosts on port 902/tcp. NBD backup throughput is typically limited to using up to 40% of the bandwidth available on the corresponding VMkernel interfaces. If NBD-SSL is enabled, the throughput is typically 10% slower than regular NBD. NBD-SSL is enforced for ESXi 6.5 hosts. Read more about this in Virtual Appliance Mode section - vSphere 6.5 and encryption.
The following sections explain transport modes in detail.