Re: ssh-vs-rsh benchmark result
Rewinding to the original post, I have a fundamental question:
Junichi Uekawa wrote:
I've tried running ssh and rsh on a local cluster, for your interest.
The experiment was ran on 60 nodes of a idle PC cluster,
each node is a dual-Pentium III 1GHz, memory 512MB,
interconnected with 100BASE-TX connection.
I have timed the following cases:
dsh -a w 3.748 -- running "rsh w" on all hosts sequentially
dsh -a -c w 1.170 -- running "rsh w" on all hosts parallelly
dsh -a -rssh w 23.051 -- running "ssh w" on all hosts sequentially
dsh -a -rssh -c w 4.306 -- running "ssh w" on all hosts parallelly
So clearly, ssh connections take longer to start.
But more importantly for us Beowulf users, who might run a job for days
and not care about a few seconds of startup time, I have been under the
impression that ssh encrypts all communications during the session,
which would use considerable CPU time in a parallel job with lots of
communication. The more communication and faster the connections (e.g.
gigabit), the more CPU time would have to be devoted to this task.
Based on this understanding, I've been putting my Beowulfs on private
nets and using rsh.
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?
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