Slow Backupspeed although 10Gbit network

[hoFFy]

Hi all,
we are currently deploying a new physical backup server at our customer. He is user 4 vSphere hosts, each is connected with one 10GBit Uplink (I know, no redundancy..). The new backup server is also connected via 10GBit to the same switch, the vSphere hosts are connected to.
We currently use network transport mode.
Because I already read a lot og times that the Management Interface of vSphere is throtteling the throughput I set up a dedicated VMKernel adapter which is connected to the same vSwitch and uses on each host the same 10GBit NIC. I hoped that this dedicated VMKernel adapter wouldn't be throttled, because I added no specials funtions to it (no management, no vMotion, or anything else).
In Veeam I added all 4 hosts with the IP address of the dedicated VMKernels, especially not using the vCenter.

But it still seems that there is some throttling active.... a single VM backup does not use more than 2GBit on the backup server, running iperf between ohne of the hosts and the backup server (also using the dedicated VMKernel adapter) shows a bandwith of ~3-5GBit.

Does this all come from throttling and will only be faster when I setup 4 backup proxies (one on each host)? If yes, why should that be faster, when also iperf does not show up more than 3-5GBit?

and yes, I didn't open a support case yet, hoping a fast answer from forum members should help.

[Gostev]

The problem is with the network transport mode itself, rather than anything else. From VMware engineering:

"This is expected behavior. According to the internal benchmarks, NFC can only use up to ~ 1.3 Gbps of network bandwidth, which is in line with 125 MBps number quoted in this SR. Increasing the maximum network bandwidth usable by NFC would require a significant rearchitecture of NFC.

As you may know vADP has different modes of transport out of which NBD is one and it uses NFC's Async IO mode. With the current architecture NFC's ASync IO mode is not capable of saturating high speed network links such 10 GbE with a single stream.

With that said, NFC re-architecture is in progress."