How does Veeam choose which ESXi server to use for NBD?

[ianmidge]

Hi. We have two ESXi 6.0 clusters (prod and non-prod) each with 4 hosts managed by a single vCenter instance. The prod and non-prod clusters connect to different storage arrays and we use a single Veeam backup server to backup both prod and non-prod virtual machines. This is a virtual appliance hosted on the prod cluster. For the prod VMs, the backup server (acting as a data mover) has access to the prod storage array and so uses the hot-add transport. For the non-prod VMs, the backup server does not have access to the non-prod storage arrays and so falls back to NBD. If I understand it correctly, the process for the non-prod VMs will therefore be:
1. Snapshot the VM.
2. Connect to an ESXi server that can access the datastore hosting the snapshot.
3. Identify changed blocks.
4. Copy the changed blocks from the ESXi server using NDB.

Assuming I have understood the process so far, my questions are:
1. How does Veeam select which ESXi server to connect to?
2. How does Veeam select which VMkernel interface to connect to?

I have spent some time searching so apologies if this has been answered before.

[foggy]

Hi Ian, if you add vCenter to Veeam B&R console, then all communication with virtual infrastructure is done vie vCenter and the particular ESXi host (the one the VM resides on) is advised by vCenter as well.

[ianmidge]

Thanks Foggy. Am I correct in saying that for a specific VM in NBD mode the transfer of data is from the ESXi host that the VM resides on directly to the Veeam backup proxy? I get that Veeam will query vCenter to discover the specific ESXi host and it makes sense to select the one where the VM resides as that will definitely have access to the backing datastores.

[foggy]

Yes, in case of NBD VM data is retrieved from the storage through ESXi network stack.

[ianmidge]

Perfect. So last question if I may. If my backup server (a VM) and the ESX server hosting the datastores of the VM I am trying to back up are connected to both a management network (1Gbps) and a backup network (10Gbps) how does Veeam choose which network to use. If it connects by resolving the DNS name provided by vCenter then that is going to resolve to the VMkernel interface on the management network which is not what I want. It would be nice if it would use the backup network but I can't see any way of coercing it to do so.

[foggy]

There's a preferred networks functionality right for this case.

[GregorS]

Ian, I presume you are aware that you can create a VMware backup proxy on the non-production cluster (or assign that role to an existing Windows VM). You will achieve way better performance with hot add. You can even add a second virtual network adapter into this proxy VM and connect it to your backup network uplink.