Reading through the What’s new document, I discovered an new feature/option which hasn’t been mentioned here before: “NBD multi-threading”
As the performance of NBD (network) in VMware backups is often not as good as virtual appliance or direct storage access storage mode, it sounded quite interesting to try. Perhaps this way we can get over some limitations of NBD mode and better utilize the network capacity of our proxies.
NBD multi-threading — The backup engine is now capable of establishing multiple NBD connections per VMDK for better performance of network transport mode. At the same time, due to the low limit of max NBD connections per ESXi host, there are reliability concerns associated with increasing the number of such connections. While our resource scheduler tracks NBD tasks per host to ensure they remain within the limit, we decided that a marginal performance benefit is not worth the risk of enabling this new behavior for our entire customer base right away, as there might be external NBD connections too. However, you can use the fully supported VMwareNBDConnectionsPerDisk (DWORD) registry value on the backup server to give this functionality a try. Our internal testing showed that the best performance is achieved with two NBD connections per disk. Please share your results in the Veeam R&D Forums to help us decide whether to enable this functionality by default in future updates!
Unfortunately I couldn’t produce any significant numbers in my lab and don’t currently have any other V11 environment where I could compare the results of using multiple NBD threads per Disk. But I still wanted to share this option here in the community. Perhaps you’ll be able to test it in your environment and achieve a slightly better network based backup performance.
As it’s a new option and disabled by default, be carefully when using it and give a feedback on your results to Veeam R&D. The only forum post I could find is this one, so I would suggest to collect all feedback there: https://forums.veeam.com/vmware-vsphere-f24/new-nbd-multithreading-feature-v11-t72689.html