mulitcast copy or snowball copy

Felix Rauch rauch at
Wed Aug 20 08:30:58 EDT 2003

On Tue, 19 Aug 2003, Guy Coates wrote:
> The only usable multicast code we've found that actually works is udpcast.
> There are plenty of other multicast codes to choose from out on the web,
> and most of them fall over horribly as soon as you cross more than one
> switch or have more than 10-20 hosts.
> We get ~70-80% wirespeed on 100MBit and Gigabit ethernet, and we've used
> it to sucessfully distribute our 60gig dataset over large numbers of nodes
> simultaneously.

That's interesting, since I tried udpcast once (just a few tests) on
our Cabletron SmartSwitchRouter with Gigabit Ethernet without disk
accesses and I got about 350 Mbps, while Dolly ran with approx. 500 Mbps
on Machines with 1 GHz processors.

I even used Dolly once (already many years ago, with 400 MHz machines)
to clone two 24-node clusters at the same time, they were connected to
two different switches and had a router in between. The throughput for
the nodes was about 6.9 MByte/s over Fast Ethernet for every of the

> The main performance killer we've found for udpcast is cheap switches.

True. I tried it once with a cheap and simple ATI 24-port Fast
Ethernet switch. Udpcast run with only about 1 MByte/s since the
switch decided to multicast everything with only 10 Mbps (one machine
that wasn't a member of the multicast group was connected with only
10 Mbps). Dolly on the other hand worked perfect with full wire speed
on that switch.

- Felix

Felix Rauch                      | Email: rauch at
Institute for Computer Systems   | Homepage:
ETH Zentrum / RZ H18             | Phone: +41 1 632 7489
CH - 8092 Zuerich / Switzerland  | Fax:   +41 1 632 1307

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