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I'm experimenting the Trinity Rescue Kit (TRK) http://trinityhome.org/Home/index.php?wpid=1&front%5Fid=12 and it's ability to clone hard disks to many computers at one time using multicast techniques. Quite cool software! All of the computers are identical and are running with gigabit ethernet cards connected to several interconnected gigabit switches on a single subnet.

I'm having an issue with the multicasting speed. If I just have the master computer and write to a single slave computer, I can image the slave computer's hard disk at over 300 mbps! But if I try to write to several of the computers at the same time the tranfer rate drops to just under 10 mbps.

The hardware and software is identical in each case and any individual slave computer gets the same 300 mbps transfer. Something about actually trying to use two or more multicast clients at the same time appears to cause it to negotiate down to the very slow 10 mbps speed.

My question is what controls the speed of a multicast broadcast? How is it adjusted? What can affect it? There are quite a few other devices attached to the switches in the office, can a client not involved with the multicast broadcast affect the speed? I couldn't seem to find any good references on the practical use of multicast so I'd appreciate some links if you have some.

Thanks!

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It probably comes from switches. Some switch doesn't handle well multicast when there is to much multicast client. What kind of switch are you using ? –  radius Aug 20 '09 at 6:08
    
The switches are all from D-Link. There is a 24 port DGS-1024D and several 5 port DGS-2205 switches. –  Scott Bussinger Aug 20 '09 at 6:31

1 Answer 1

Multicast is very hard to handle by switch. A cheap switch like DGS-2205 will not be able to handle multicasting to too many port at one time. I don't know performance of DGS-1024D but it's a cheap switch too so don't expect to be able to send lots of multicast to many port at the same time.

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Well, the multicast did function to at least the 6 clients I tried it with. It just did it slowly. Is that typical of multicast? While I don't doubt that inexpensive gigabit switches are limited compared to more expensive models, what feature on a spec sheet would you look at to determine suitability for multicast? I looked at both the spec sheets for those routers and at the specs for several other routers and none of them mentioned it at all. –  Scott Bussinger Aug 20 '09 at 15:24
    
Yes multicast performance is never on spec sheets, this has to be done by yourself or you should try to find test result on internet –  radius Aug 21 '09 at 7:30
    
I asked D-Link about it and the switches convert the multicast into broadcasts. No explanation yet on why the 10 mpbs speed or why a single multicast recipient seems to work at full speed. It's possible the software itself handles this case differently. –  Scott Bussinger Aug 22 '09 at 22:20

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