By default, the transport mode is selected automatically for backups and restores, based on the VSA proxy used and the virtual machines being backed up or restored. You can force a specific transport mode by configuring it at the subclient level, or by configuring an additional setting for all proxies that are used by a vCenter client.
The following transport modes are available in VMware. Advanced transport methods (SAN and HotAdd) replace the proxy-based VMware Consolidated Backup (VCB) solution.
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SAN (storage area network) - SAN mode is supported for directly connected storage using Fibre Channel (FC) or Internet SCSI (iSCSI) protocols. With automatic transport mode selection, SAN mode is selected if SAN storage is connected to the ESX host. 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.
Notes
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SAN transport mode is only supported for proxies on physical computers, and cannot be used if the proxy is a virtual machine.
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Changed Block Tracking (CBT) is disabled for SAN transport writes because the transport mechanism must account for thin disk allocation and clear lazy zero operations.
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SAN only supports writing to base disks; it does not support writing to redo logs for snapshots or child disks.
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SAN transport mode is supported for SAS data stores.
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SAN transport mode is not supported for VSAN datastores.
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HotAdd - In HotAdd mode, the Virtual Server Agent is installed on a virtual machine residing on an ESX Server. The term HotAdd refers to the way the backups are completed. In HotAdd mode, the data volumes containing 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 the proxy is running 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. If SAN mode is not available, HotAdd mode can achieve close to SAN mode performance.
Note
Licensing. In vSphere 5.0, the SCSI HotAdd feature is enabled only for vSphere editions Enterprise and higher, which have Hot Add licensing enabled. No separate Hot Add license is available for purchase as an add-on. In vSphere 4.1, Hot Add was also enabled in the Advanced edition. Customers with vSphere Essentials or Standard editions are not able to perform proxy-based backup, which relies on SCSI HotAdd. Those customers must use alternate transport modes.
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Local Area Network (NBD and NBDSSL) - NBD (network block device) & NBDSSL (encrypted NBD) transmit data over the TCP/IP connection between the ESX server and the proxy computer. NBD serves as a fallback when other transport modes are not available. The local area network (LAN) can be the production network or a dedicated backup network.
NBDSSL is 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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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).
The following table summarizes the configurations based on the storage type:
|
Mode |
Datastore Storage Type |
VM Data Protected by Single Node |
Additional Comments |
|---|---|---|---|
|
LAN Free SAN mode |
VMFS using Fibre Channel or iSCSI |
Up to 40 TB |
Virtual Server Agent and MediaAgent installed on the same physical computer with direct connection to datastore. Eliminates data transfer over network during backup and restore. Provides best backup and restore performance. |
|
LAN Free HotAdd mode |
VMFS, NFS, VSAN |
Up to 30 TB |
Virtual Server Agent and MediaAgent installed on virtual machine running on host with access to datastore. Eliminates data transfer over network during backup and restore. |
|
Network based (NBD, HotAdd, NAS) |
VMFS, NFS, VSAN, direct attached storage |
Virtual Server Agent and MediaAgent installed on different computers. The Virtual Server Agent writes over the network to a remote MediaAgent. Depends on infrastructure. Not recommended except with exceptional VMware configurations. |
In most scenarios, backups and restores using SAN and HotAdd transport are faster than local area network (LAN) operations using network block device (NBD) or secure NBD (NBDSSL). SAN restores using thin disk provisioning can be slower than LAN restores; performance can be improved by using NBD or by setting the transport mode to SAN and forcing the disk type to thick, which uses eager zero provisioning.
Connectivity
Configure DNS on the backup proxy, ESX hosts, and vCenter Server. For any transport mode, missing or incorrect DNS configuration produces nslookup errors during fully qualified domain name (FQDN) resolution.
Related Topics
Troubleshooting articles: