@plegrand said in Multicast very slow:
Then there is 2 sessions running (test and test2) and all the target computers have about 1.15GB/min rate
Just so I’m clear on this. When you were able to get 4 computers imaging your transfer rate was 1.15GB/min? That’s still 19MB/sec. You are still above the 100Mb/s theoretical limit.
All the computers have 2 partitions and strangely the first partition is slower than the second : about 700MB/min rate
I can explain this. The number is based on an incorrect calculation. The issue is that first partition is pretty small, like 500MB. It transfers so fast that the speed numbers get skewed. The second partition is typically the contents of the 😄 drive. You can see this if you look at the disk manager in Windows. Look at the size of the first partition.
I might need to explain how image multicasting works. There is one computer (FOG Server) that is sending the image out. As each multicast client boots up it checks in with the multicast sender through a discovery process. The muticast sender (FOG Server) configures the multicast sender service to wait for X number of clients to check in before going, or after the first client checks in wait for XX seconds before going even if not all have checked in. Once the multicast stream starts, no other late clients can check in (they are blocked). So in the image stream the FOG server sends out the first block of data then stops. It waits for every multicast receiver (target computers) to respond with “OK!”. The FOG server will not send the next block until it hears “OK!” from every client. If something happens and one client didn’t get the block correctly it will send “Retrans” back to the FOG server and the fog server will resend that block back to the client computer (while the others sit and wait until everyone replies with “OK!”. This is why we say multicasting can only go as fast as the slowest computer in the multicast stream. Consider you have 4, 8-core desktops all with SSD drives and one with a Penitum-4 and a slow HDD. If you imaged them all in one stream the 8 core systems would image at the rate the Penitum-4 system can write data to its slow HDD. If you have a system with a failing hard drive if the block transferred to it’s checksum doesn’t match the checksum of the block on the disk it will send a “Retrans” command back to the FOG server while the other clients wait. The point is when everything works it works well, when you have one bad actor everyone suffers.