[Beowulf] ethernet bonding performance comparison "802.3ad" vs Adaptive Load Balancing

Rahul Nabar rpnabar at gmail.com
Thu Sep 18 15:08:24 EDT 2008


On Wed, Sep 17, 2008 at 11:25 PM, Martin Siegert <siegert at sfu.ca> wrote:

> It is my understanding that 802.3ad forbids what you want to do:
> running a single stream over more than one link; 802.3ad requires
> that all packets are guaranteed to be delivered in order.

Yes, you are probably right Martin. I didn't know much about the
802.3ad at all until very recently. But the iffy point seems to be the
definition of a "single stream" Does it mean "all traffic from a
computer" or "all traffic from one process" or "all traffic from one
protocol"

I guess that's the crucial question for my need right now.

> This does not mean that you cannot do what you want: you need to use
> round-robin mode (which AFAIK is still the default under Linux;
> easy to test with crossover cables).

Sure; mode_rr is always around. [I didn't get the test with the
crossover cable though, sorry, could you explain perhaps? I'm not at
all a networking guy  ]

> - most switch vendors do not support round robin mode - the only one
>  that I know who does is Extreme (please correct me!).

That brings me to the other question though? Does mode_rr "need"
switch-support? (ah! perhaps you mean I'll get assymetricity? Transmit
side load balancing but no receive side load balancing because the
switch will insist on sending all packets to a machine over a single
port. Unless my machine answered ARP requests from different machines
with alternate MACs of its cards and thus fools the switch into. But I
guess that's what mode=6 does! So I'm not even sure how that is
different from mode_rr. I'm sorry I'm confused again! ) Aren't many of
the modes designed to operate inspite of an ignorant switch? I'm never
sure which ones though!

>  You can get around that problem by using a separate switch for each
>  leg, but that requires that each host has the same number of interfaces
>  for that bonded network. E.g., you cannot have a host with a single
>  10GigE card and another host with 4 1GigE cards.
>

Ah! True. I do have two switches here and each of my nodes have two
eth cards. So I guess I could do that too.

-- 
Rahul
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