Robocopy performance issues?

Question

Backup

Good afternoon, dear ones!
Please advise on the operation of the robocopy utility.
1. There is a Windows file server (Share) with public network resources. Resources are located on iSCSI LUNs on the storage system.
2. An iSCSI LUN (X:\) is connected to another Windows server (Backup) for backup and robocopy is started from this server.
Robocopy copies from \\share\folder to iSCSI LUN (X:\). At the same time, there are serious problems with copying speed = 10-15 Mbps. If you manually copy the file (Copy-Paste), then everything flies in an instant.
If the backup LUN is connected directly to the file server and copied without using network paths, then the situation improves significantly and, judging by the utilization of the channel, copying occurs at a speed of 1-2.5 Gbps.
Tell me what could be the problem? Or is it a feature of robocopy in UNC work?
What other tool can be used?

Answer 1

Check network speed with iperf

Answer 2

Good afternoon!
Measured the speed with iperf. Values ​​2.3 Gbps - 3.9 Gbps.