@vemoya Well 3 GB/s is on the bottom edge of acceptable (in my book). There may be some tuning needed to do in your infrastructure. Its not horrible just a bit slower than expected.
Just be aware with 3 ongoing unicast images you will saturate a 1 GbE link (125MB/s or 7.5GB/min theoretical max) This isn’t a fog issue specifically but a limitation of 1GbE ethernet. You can supplement this by adding additional network cards in your FOG server and then creating LAG links between your network switch and the FOG server. Even if you create these LAG links between the FOG server and switch, if your switch to switch links are 1GbE links that will become your next bottleneck. Again this isn’t a FOG issue, but a byproduct of using a FAST imaging solution. Also if you are imaging more than 2 computers at a time, its best to have an SSD or RAID array in your FOG server and not try to serve multiple unicast streams with a single spindle HDD. That single HDD will not be able to feed the data fast enough to the network adapter.
You mentioned multicasts. This is a great solution to push out one image to many computers, but it also has its drawbacks. You need to ensure your network is capable of multicast imaging (again not a fog issue). If your target computers are on the same subnet as the FOG server that is the easiest solution. You just need to turn on IGMP Snooping on your network switches and then multicast away. Just remember the slowest computer in your multicast group sets the pace for the group. But if properly setup you can multicast 30 computers in about the time it takes to image 2 computers (serially) using unicast imaging.