Experts opinion on client server interface vs network interface

When Nicolai says "LACP is not as effective as 10G, but much better than 1G."

...I think he is referring to this:

Balance-alb bonding wouldn't normally be used because balance-alb manages ARP replies from different hosts.  As ARP requests are only ever sent to devices on the local LAN ‘IP Subnet’ that means that balance-alb will only provide balancing for local IP addresses.  All other requests off of the subnet will go to the same NIC as they will all originate from the same source, i.e. the subnet’s gateway.

It is better to implement bonded resiliency and balancing by using LACP and thus have the LAN switches load balance across the links to the backup server/appliance.  Using the ‘source and destination IP’ configuration of LACP will result in a fairly even distribution across all links.  Although the destination IP address will always be the same, the source will vary and thus result in some variation - but note that LACP is not guaranteed to always result in variation.

The net effect of say 4x1Gb in an LACP bond is that you cannot guarantee to get 4Gb ingest at the backup server.  Sometimes four backup clients will be spread nicely across the four links, and sometimes the four backup clients will be assigned to just one of the 1Gb links of the backup server, and so each client will only get around 300Mb/s, and the other 3 x 1 Gb NICs on the backup server will sit there doing nothing.  So, if you need to get closer to guaranteeing that many 1Gb based backup clients can all get close to concurrently sending at 1Gb and that NetBackup server/appliance can get close to concurrently receiving at 4Gb, or better still exceeding this, then you need at least one 10Gb link on your backup server.

HTH