Recently I encountered an issue with dreadful disk digest speeds while running a Veeam replication job. It was taking days to digest a 100GB VMDK. I had over 3TB of data to digest so this simply was not acceptable.
Further troubleshooting revealed the Veeam proxy being bottlenecked by a 100mbps switch located at the DR site, the proxy was virtual and the virtual machine traffic port group was on a separate vSwitch to the management traffic port group.
After moving all the replica VMs across to the one host, consolidating the port groups into the one vSwitch (configuring correct NIC active/standby is very important here) and rerunning the jobs the disk digest performance improved drastically. It is now looking to take around 10-14 hours compared to a week.