In a shared VMware environment with self-service capabilities, tenants are responsible for backup job scheduling. As an outcome, the considerations for proxy modes can be different from a fully managed environment:
Direct SAN/NFS The core shortcomings of Direct SAN/NFS mode are the requirement of backend infrastructure and initial configuration overhead. More details are highlighted in the user guide.
NBD (network mode) This mode doesn’t have any special setup requirements. The main consideration of using NBD is network capacity (10Gb of faster ). More details are highlighted in the user guide.
In this mode, VM disks are attached (hot-added) to the backup proxy and data is transported to the target location. Once backup or restore is finished, VM disks are detached from the backup proxy. This process can take 1-2 minutes per disk. It can take a significant time on a large quantity of VM, so backing up 100 VMDKs potentially adds 100-200 minutes to the backup window.
Massive VMs are rarely seen in shared environment. On another hand most tenants, create sets of small VMs. This is where Hot-Add can bring management overhead during the backup process.
However, due to the specifics of VSAN, in such environment Hot-Add is still the recommended mode.
Backup from Storage Snapshots (BfSS)
This mode is recommended when backup jobs are created based on datastores. In a self-service environment, this is impossible to control. Therefore the best practice is to avoid using storage snapshot integration as a mass offer. However, it is recommended to offered it as a separate service for VMs with very high change rates. In this case, configuration should be done by service provider.
More details on the reasons are highlighted in VBR Best Practice Guide