How to locate bottlenecks for backups

[dimaslan]

We are an MSP and we have our own datacenter. We recently upgraded our two Synology (RS3621RPxs and RS3621xs+) with 10Gbit connectivity.
Our backup servers are vms on a single esxi also with 10Gbit connection.
One NAS has 24 disks (main storage + 1 tray) and the other has 12 disks on the main storage.
I am seeing though that I am not getting better speeds. What path would you go with to investigate where there's a bottleneck if there is one?

[karsten123]

iscsi? NFS? What type of HDDs?
Backup servers equal repositories?
Did you maxed out the system memory of the Synologys?
Real numbers of the speeds?

[Andreas Neufert]

Veeam Jobs always have bottleneck Analyze where the highest value shows identifies the bottleneck in the job statistics.

This gives you an indication where to search for.