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Re: ssh-vs-rsh benchmark result

Le vendredi 30 août 2002 09:46 -0400, Adam C Powell IV écrivait:
> Rewinding to the original post, I have a fundamental question:
> Is my basic understanding sound, or does ssh send the session info, X 
> stuff, etc. in the clear?  Or does this not add significant computation 
> time, e.g. on the order of what the kernel uses to get the packets out 
> through the NIC?  Has anyone seen/done relevant benchmarks which would 
> test the magnitude of this effect?

SSH encrypts the whole connection. And it's very CPU intensive. Here are
a few results I obtained when I did some tests :

Configuration : file transfer from an AlphaServer ES40 with 4 EV67 to an
SGI Origin 2000 with 4 MIPS CPU through a HiPPI network. The
pseudo-benchmarks were done on a busy machine, so they're not really

Transfer of a 1 GB file in chunks of 512 KB :

dd if=/dev/zero bs=524288 count=2048 | R_COMMAND origin2000 "cat > /dev/null"

The results are the following :

With R_COMMAND == rsh : ~ 50-60 MB/s

With R_COMMAND == ssh -c 3des : ~ 1-2 MB/s !!!

With R_COMMAND == ssh -c blowfish : ~ 4-6 MB/s !!!

Clearly, SSH is a real hog on performance. While doing the tests, I also
noticed that a full CPU was busy on the slowest machine (SGI) while
doing the transfer. The other one was 35% busy... The bottleneck is now
the CPU and not the network. Even with a faster algorithm (blowfish
instead of 3des), ssh is 10 times slower than rsh and uses a lot of CPU

Maybe the processors on the SGI are old and not up to the task (I think
they are 250 MHz CPUs). Maybe you can still saturate a 100Mb Ethernet
with a Pentium IV machine with SSH, but the CPU price seems high.

Those "benchmarks" were done with file transfers, but it seems that with
a parallel program with a lot of communications, it is a bad idea to use
SSH to do the communication.

Alexandre Vitrac
OpenPGP key ID : C03A7DFE

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