This section discusses the various advanced transport mechanisms, and other backup issues.
VDDK 5.0 contained two new VixDiskLib calls (PrepareForAccess and EndAccess) to deactivate and re-enable Storage vMotion during backup. This prevents stale disk images from being left behind if a virtual machine has its storage moved while a backup is taking place. VMware strongly recommends use of these calls.
When an ESXi host is managed by vCenter Server, vSphere API calls cannot contact the host directly: they must go through vCenter. If necessary, especially during disaster recovery, the administrator must disassociate the ESXi host from vCenter Server before the host can be contacted directly.
Advanced transports allow programs to transfer data in the most efficient manner. SAN transport is available only when the physical-machine host has SAN access. HotAdd works for the appliance model, where backup is done from inside virtual machines. HotAdd requires the virtual machine datastore to be accessible from the backup appliance. NBDSSL is a secure fallback when over-the-network backup is your only choice.
SAN transport is supported only on physical machines, and HotAdd transport is supported only on virtual machines. SAN requires a physical proxy to share a LUN with the ESXi host where a datastore resides, enabling direct access to raw data, and bypassing the host altogether for I/O operations. HotAdd involves attaching a virtual disk to the backup proxy just like attaching the disk to a virtual machine.
