Rahul Nabar wrote:
I was experimenting with using channel bonding my twin eth ports to
get a combined bandwidth of (close to) 2 Gbps. The two relevant modes
were 4 (802.3ad) and 6 (alb=Adaptive Load Balancing). I was trying to
compare performance for both.
Before running any sophisticated tests by netperf etc. I just tried to
copy a large file via scp and timed the two file-copies.
Option1:
from node1 to node2. Both nodes have their twin ports bonded together
as bond0 with mode=4 (802.3ad).
They are connected via a Dell PowerConnect 6248 switch. Configured the
switch so that I have two LAG groups combining the two ports coming
from the same node. LACP was turned on.
Option2:
from node3 to node4. Use mode=6 (alb=Adaptive Load Balancing) No
special switch config. No LAG. No LACP.
Result: For a 4GB file-transfer. Both modes took the same time; approx
1min26 sec.
These results are very mystifying to me. I was expecting mode4
(802.3ad ) to be almost twice as fast since it is the only mode which
truly aggregates the twin channels. It ought to be the only one
effective for a peer-to-peer communication (mode 6 would only help
while talking with more than one peer)
Any comments? Also the net file transfer speed seems way lower than
what I'd expect from a close to 2 Gbps connect; even accounting for
the protocol overheads. Do other people have some numbers for me from
their systems?
Well, apart from the fact that ssh is compressed and, as Digo pointed
out and that 47 MB/sec is probably your HDD's transfer capacity as
Shannon pointed out, also keep in mind your bus's capacity (
http://en.wikipedia.org/wiki/List_of_device_bandwidths is a nice list).
So, unless you've got both NICs on PCI-E (or independant PCI channels,
which I've only heard of in high-end Compaq servers with hotswap PCI
interfaces) you're saturating your bus.
Eric
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