Should multicast speeds be comparable to unicast?



  • Server
    • FOG Version: 1.4.0 fresh install
    • OS: Ubuntu 14.04.5
    Client
    • Service Version: not sure
    • OS: Win10 image to be deployed
    Description

    Hello, everyone. I had a question about multicast speeds. I have 20 machines set to image via multicast on a Netgear ProSafe S3300-52x switch. When I use multicast it transfers at about 2.30 ~ 2.32 GB/s. When I deploy a single image, it transfers at about 5.80 ~ 5.90 GB/s, and starting additional unicast transfers will still go 5.30~5.40 GB/s, but will start to drop off significantly after adding 3 or 4 more clients. Multicast definitely seems like the way to go when doing 10 or more computers, but is there a way to speed up multicast? I thought theoretically I should be getting closer to unicast speeds.

    My network setup is pretty basic. All the machines in play are on the same switch and the switch is set to default settings. Is there anything I could tweak on the switch to speed it up? It doesn’t do anything besides provide network to the imaging bench.

    Any input would be greatly appreciated. :)



  • HenryI did an experiment, a simple multicast send and receive on a private network contains only the Access Point and one station. The results are:

    1. With the station sends and the Access Point receives multicast data using 224.0.0.1, the rate is over 20 Mbit/sec.
    2. With the Access Point sends and the station receives multicast data using 224.0.0.1, the rate is over very slow even less than 2 Mbit/sec.
      I have no clue!!

  • Moderator

    @forte647 It’s also worth noting that multicast has some overhead that unicast does not have. But even with this, you will get large bandwidth & time savings when imaging 100s of boxes at once.



  • Thanks for the info. It might be an underpowered CPU on the switch. All of my cables are fresh and give around 5.8 gb/s unicast, and all of the hardware I am imaging to is fresh out of the box.

    Have a good week!


  • Moderator

    @forte647 said in Should multicast speeds be comparable to unicast?:

    Netgear ProSafe S3300-52x

    Different switch models perform differently with multicast even though they advertise 1Gbps port speeds.

    Switches with underpowered CPUs will perform worse, while switches with higher powered CPUs perform better. Why is this? Because with multicast, the switch has to use CPU cycles to duplicate the packets to all ports. This is a CPU-intensive activity for the switch.

    I wouldn’t think the Netgear ProSafe S3300-52x is underpowered - but when the manufacturers don’t list the CPU specs or total throughput capabilities on the tech specs page we are left wondering.

    Also, multicast can only go as fast as the slowest member. So if one of the members in the multicast group has a bad stick of RAM or a failing disk or a bent & kinked patch cable, that box will slow the entire group down to it’s speed.


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