When you restore a VMware VM, you can specify the transport mode.
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Auto: The transport mode is selected automatically based on the backup environment:
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If the datastore is accessible to a physical proxy, SAN is used.
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If the datastore is accessible to the ESX server for a virtual proxy, HotAdd is used.
Otherwise, NBD is used.
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HotAdd: The Virtual Server Agent is installed on a virtual machine residing on an ESX server. In HotAdd mode, the data volumes that contain the virtual machines to be backed up are automatically mounted to the proxy, so they can be accessed by the proxy as a local disk. The ESX host that the proxy is on must have access to all datastores for the virtual machine. If the virtual machine and the proxy are not on the same host, all datastores must be shared between the hosts.
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NAS: NAS (network attached storage) transport mode enables the virtual server agent (VSA) proxy computer to read data directly from the network file server (NFS), without going through an ESX host or transferring data over the local area network (LAN).
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NBD: Data is transferred using the TCP/IP connection between the ESX server and the proxy computer. The local area network (LAN) can be the production network or a dedicated backup network.
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NBD SSL: Similar to NBD mode, but data transfer between the proxy computer and the ESX server is encrypted. Encryption should be used for sensitive information, even within a private network.
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SAN: For directly connected storage using Fibre Channel (FC) or Internet SCCI (iSCSI) protocols. The Virtual Server Agent must have access to the datastore LUNs (logical drives) that provide storage for virtual machine disks. Data is read directly from the storage where virtual machines reside, without going through the ESX host or transferring data over the local area network (LAN). The ESX host is contacted only to coordinate access to the LUN. SAN transport mode cannot be used if the proxy computer is a virtual machine.