Yes, that's true, using the NBD with the current separate subnet of VB4.0 physical backup server and the SAN, I've got like:
22 of 22 VMs processed (0 warnings)Details
Total size:792.0 GB Processed size:712.0 GB
Processing rate:15 MB/s Total time:13 hours 54 minutes
so in this case you're all not alone in this matter.
Next time I'll try to use with vStorage API and make the backup server in the same subnet as the iSCSI SAN.
/* Veeam software enthusiast user & supporter ! */