SAN Transport for VMware

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.


  • SAN transport mode is only supported for proxies on physical computers, and cannot be used if the proxy is a virtual machine. Use a HotAdd configuration to deploy a proxy on a virtual machine.
  • SAN mode is not supported for vSAN datastores.
  • You can use the VMFSSanInfo Tool to get information about the mapping between physical disks and datastores.

SAN Transport Scenarios

LAN Free Backup for SAN-Based Storage

LAN free backup is used automatically when:

  • Virtual machines to be backed up are on SAN datastores.
  • Each proxy that performs backup operations is a physical server.
  • The Virtual Server Agent (VSA) and MediaAgent are both deployed on each proxy.
  • Each MediaAgent has local access to directly connected storage using a shared mount path.

During backup, the VSA reads the virtual machine disks (VMDKs) directly over the SAN, performs block level deduplication, and sends the data to a local MediaAgent that writes to the shared library. SAN transport mode provides the fastest method for full or incremental backups because data is not sent over the LAN. Data is never transferred over the IP network, except when the library is configured on a network-attached storage (NAS) device.

Physical Proxy Installations

In a physical proxy configuration, the Virtual Server Agent and MediaAgent are installed on a physical server with visibility into the storage network. A purely physical implementation performs SAN-only backups and usually provides the best performance.

When to Use

  • Datastores are configured on Fibre Channel (FC) or iSCSI SAN.
  • Physical server has SAN access to datastore LUNs.
  • Direct tape copies are required or physical MediaAgents are required for secondary operations.

When Not to Use

  • SAN access to datastore LUNs is only available within the ESX Server environment.
  • SAN transport is not available for storage accessed using the Network File System (NFS) protocol.

Best Practices for SAN Transport

  • SAN transport generally provides the best performance for thick disk restores, but the worst performance for restoring thin disks. For thin disk restores, NBD or NBDSSL is usually faster.
  • When using SAN transport during restores, the restored disk size must be a multiple of the underlying VMFS block size. The restore adds zeros to complete the block (not applicable to eager zeroed thick disks).
  • For Enterprise and Datacenter editions of Windows Server 2008, the default SAN policy is offline. SAN policy should be set to onlineAll for Windows Server 2008 proxies, and SAN disks should be set to read-only except for restores. The diskpart utility can be used to clear the read-only flag.
  • For Linux proxies, you might need to rescan the SCSI or iSCSI bus after attaching devices.

    For MediaAgents on the Commvault HyperScale 1.5, you can use the rescan-scsi-bus.sh script to force a rescan.

Related Topics

Troubleshooting articles:

Last modified: 1/15/2020 8:16:02 PM